I too recently purchased a '96 S420 with 70k+ miles.
My c/u offered a warranty that is good up to 100k, after that you're on your own.I also looked for aftermarket extended warranties.They were very expensive for my car($2800us) for
12 mos or 12,000 miles.I don't know about you, but I bought a
Mercedes to put 20k+ miles a year on it.So this option would get expensive real quick.
Yes W140s are expensive to repair,but they are worth
it.Comfort,confidence,and pride have a price.Just had to replace
rearview mirror to the tune of $800.NO REGRETS.
If you still want to shop for yourself; do a search for
extended warranties.I went to(browse only) warrantybynet,
platinumplus,etc........the problem(expense) lies in the mileage
of our cars.I think for owners of lower mileage cars there may
be deals out there.Good Luck