I tried your first option and did not work.. floor not rusted enough.
Will try your other options..
Thanks for the advice

Start with a small bit to make a pilot hole just deep enough to hold the bit from wobble. Work your way up in bit size until the hole in the top of the bolt is large enough to pop loose from the threaded end of the bolt.
I like to use left hand drill bits - about half the time, the bolt will back out before I get the hole drilled.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html