I have two 85 300d's one is a grey market and newest one is American. I bought this car from an online dealer auction cheap. It has 145,000 miles and perfect leather interior and excellent paint. All systems work such as the cruise control, tach, all gauges, heat and air. In most respects it is much better than my grey market. The main problem as in most 300d's is the trunk. Both wheel wells are rotten. The rust is only in the wells not on the outside body panels. I am considering keeping this car and selling the grey market. What I am wondering is, How much can I expect to pay for the wheel well repair? Both sides need replacing. By the way I see no other rust on the car except for 2 two or three small rock chips. Thanks in advance for all your advice.

I would clean the wheel wells up as best as you can and coat then with POR15. It only requires that you remove the loose scale. Are you sure there was not an earlier repair? These are prone to this problem.
Ron

I sure it has not been repaired before, I might be able to use the POR15 on the driver side but the passanger side is really bad, I can push my finger through some of it.

This is a unibody car and wheel wells may be structual. If car has had a repaint at some point check the outer wheel well flange with a magnet. If the outer flange is okay start to probe inner wheel wells as some just have rust an inch or two in past the outer lip. For those an aftermarket patch panel is available punched out to about five inches depth that can result in a good economical repair. These patch panels are made in denmark and available through most UAP etc type places.(20-30.00 per side) If the whole wheel well is rotten that is a different story. Again if you can see that the car has had a repaint at some stage get it up on a hoist and start looking around the jack points, general rocker panels, floors etc very careully. In fact probe with screwdriver or pick. I have one 240d with this rust pattern in storage waiting to get to it. Rear inner fenders are rotten for about the first two or three inches in. Seem solid past that. Outer fenders are rotted for about 2 inches up as well. Floor, trunk and rest of wells are just about perfect so will weld inner and outer patches in and paint. Rust patterns seem to vary all over the country and even find different patterns in same areas sometimes. Just strange. Just like yours I picked up very cheap but vendors did not realise it had a brand new engine and had always been mechanically maintained by a mercedes dealership with no expense spared and the interior was still like brand new it shows 240k. Only prior repaint was one front fender that got dinged or changed and repainted because of rust.

Barry, thanks for the help. I don't think the car has been repainted but I will use a magnet to verify. I think this car is worth fixing. There is no rust anywhere else. Since I only paid $750.00 for the car I have some room to work and not be upside down. I don't think I can say that about my grey market.

Yes, sounds by your description you got a pretty good one. The inner fender patch panels are a lifesaver and really not that bad to install. If they were not available I would have had to get the metal cut out of a junk body with no rust and shipped to me as i live in the real rustbelt. If I lay in bed on a quiet evening you can almost hear any car parked outside rusting away. Have a good look around your front and rear rubber window surrounds for any evidence of paint on the rubber. Even a trace means it has been repainted. Many times when asking a vendor in states if car has been repainted they would quote they did not know. Nice to hear someone gets a break once in awhile. This site is the best auto related I have ever seen by far. If I need to know something it is either going to save me time or/and money to say the least. Plus the unusual is presented well. Knowing the common failure modes or weaknesses in this models design are also well presented. The common pool of knowledge is strong enough to allow individuals to learn and develop confidence in what they are doing as well. I go into perhaps too much detail as the person that I am responding to may have less knowledge than myself but the majority have more. Just hope I do not overdo it.