81 300D Prone to leak? (floorboard rust problems)

I've heard that older MB's are prone to leak. Other day my friend jumped in the passenger side seat and said the seat felt loose and lopsided. Lo and behold, upon examination,
the floorboard along the passenger door is rusting out! The
rear right bolt for the seat had completely busted through the
floorboard. I think I can at least bolt a plate in it's place, but I can't seem to be able to find where the leak comes from. Anybody know where these models are prone to leak? In fact it rained a lot last night, and I don't see a wet spot in there. I wouldn't think the rust came from outside in, but maybe I'm wrong.
Thanks, Phill
261, 000 mi

[Ken300D]

There is a lot of information on this site about W123 body rust. Just use the search engine. There is one thread in particular that shows pictures of someone rebuilding their floor with sheet metal.

Leaks usually come in around the windshield gasket and can also occur if the drain holes under the hood hinges are blocked. Leaks in the back come in around the back glass seal.

On my '82 300D, I am planning a rear glass seal replacement later this year. My floorboard is unrusted and I want to keep it that way.



Ken300D

[engatwork]

I had the local SafetyLite glass store replace the front/rear seals on the 240D prior to selling it to my sister. They charged $75/each to replace them which I thought was a fair price. Looking at the chrome trim around the windshield you can't even tell it has been removed/replaced.

[engatwork]

Yep - $1.00 and I got a written agreement that I would purchase it back for the same amt at the end of the summer (no later thatn Oct 1st - when it cools back off ). This way I have no liability for it while they are using it.
I stopped by their house this am and checked the fluids, etc... Everything looks good.