Rust

Rust is the Miata's long-term problem, and most of it starts where water gets trapped. This page says where owners say it starts, what they do to slow it, and which repair panels are for sale. It is not a repair guide, and a bad case needs a body shop.

How to read it. The owner accounts are from one Miata.net forum thread (NA, February 2015, started by a Pennsylvania owner) that I read in full on 1 October 2026, and from one site article. Panel descriptions are the sellers', read on their own pages that day. There are no prices on this page.

Where it starts (NA, from owners)

• The lower rear quarter panel, ahead of the rear wheel. One poster, a long-time owner, called this the most common first place. It is not the rocker: the quarter panel's lower part covers the rocker panel and is spot-welded to it, and dampness gets between the two. It first shows as bubbles in the black stone-chip area low on the body, then spreads up and forward toward the rocker under the door.
• The lower front fenders. A second poster who had bought five Miatas removed the two bolts at the bottom of each front fender on every one and found a handful of wet leaves, dirt and sand in each. Both posters say to hose that cavity out regularly.
• The rockers and the rest of the rear quarter. The same poster expects almost any 20-year-old car with 100,000 miles to have some rust forming in those places.
• The trunk. One poster says rust holes in the trunk are rare.
• Inside. Posters say bubbling usually means worse underneath, and one says all of them are rusting inside, only to different degrees. Salt is the multiplier: one says that if you repair rust and keep driving on salted winter roads, expect to repair more.

How owners slow it down

• Wax-oil, not undercoating. One poster says rubberized undercoat prevents nothing, and that a wax-oil type spray (he names LPS) is what to put in the rockers and the lower rear quarter, because it creeps between the panels. Mazda sprayed something like it at the factory, he says, around the trunk sides, the doors and into the rockers, but not enough. He says you can make it at home.
• Reaching the lower quarter. His method is to drill a hole in the front of the rear wheelhouse, spray wax-oil in so it runs down to where the quarter covers the rocker, and plug the hole. He also says to seal the gap between the inner and outer rear wheel arch panels, all the way round the wheel opening, with body caulk or silicone-latex caulk.
• Rust converters for panels you can reach. The other poster uses a rust-proofing system (POR-15) wherever he finds rust in the front fender cavities, and names Eastwood's rust encapsulator and a product called Miracle Paint. The first poster agrees such coatings suit panels you can get to, but not the quarter panel where it covers the rocker.
• Keeping the cavity open. The second poster puts anti-seize on the fender bolts and two small stainless washers per bolt between the fender and the chassis, so the fender does not seal tight against the body and trap water, and still cleans the cavities at least once a year. That is one owner's habit.
• Top drains. Keep them clear, since blocked drains put water into the sills; see soft top drains.

Checking, and what repair means

• Looking inside a rocker. One poster says to take off the plastic sill (threshold) cover, about six screws, and shine a light into the slotted holes under it. Factory wax-oil usually makes the rocker itself look fine. A car with no bubbles in the stone-chip area is, in his view, probably sound for a while if kept out of salt and treated.
• Underneath. The same poster says surface rust on nuts, bolts and parts is normal, but heavy rust is a reason to think twice.
• Buying. Posters suggest an independent inspection on a lift, and showing photos to a body shop for a worst-case quote.
• Repair. Posters say any rust is fixable with enough money, that a patch fails if the welder does not remove every bit of rust, that the back of a welded patch is prone to rust unless treated, and that covering rust with body filler without converting it hides a growing problem.

NB, NC and ND

For the NB, the article NB Miata Troubleshooting (Worth Driving, updated October 2024, a site article with no named author) lists rocker panels, fender arches and front frame rails, and says rocker rust can develop inside unnoticed. It advises rust-proofing and clear top drains, and says a fix means cutting out and replacing panels. I found nothing specific on the NC or ND beyond a general NC owner's guide the app already cites, and no NC or ND repair panels.

Repair panels for sale

These are steel repair panels. Moss says its fender repair panels should be welded in by a professional; the other pages did not say how theirs are fitted.

Named in search results, not opened

Rev9 Autosport sells rocker repair panels, including a metal one for the NA and fiberglass ones for the NA and NB (metal, fiberglass); its pages refused my request. I did not open them, so I cannot say what the sellers claim. eBay also lists rocker and arch panels for the NA; I did not open those.

Not covered yet

• Where to buy the wax-oil sprays and rust converters the posters name; I did not open any seller for them.
• A body shop or welder who has done Miata rust. None is named in the thread.
• NB lower rear quarter panels and front frame rail repair sections, and anything for the NC or ND.
• Owner accounts of fitting the panels above, and of how well they hold up.

© 2026 Fischer Interactive LLC. Written for the Ref Sensor app's Miata users. The seller's page is the authority.