I'm not an expert, but I bought a 1980 450SL about a year and a half ago, and I can share with you the problems I've had. Mine too was in relatively good shape, especially the interior. I purchased it w/ 92k miles on it, so the mileage is about the same as yours.

I'd say the biggest thing to look at is the AC. I bought the car from my grandpa who lives in a cool place and never used the AC. First summer here I found out it didn't work. $2300 later, it was fixed.

I've had a problem with the antenna not wanting to raise up all the way. To fix it right, it costs about $300.

I do from time to time find little areas of rust that I never saw at first.

The only other problem I have experienced was a clogged fuel injector. Got it fixed for a very reasonable $65.

I've found that the car really likes to be driven. It runs better when I drive it regularly. The clogged injector probloem surfaced after the car sat for about 6 weeks during winter. I try and drive it at least once a week now.

Hope this helps a little.

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Chris Meyer
1980 450 SL (99k miles)
2003 Honda Odyssey (Family Hauler)
2006 BMW 330i (daily driver)