Mercedes Benz repair: 1983 mercedes 240d, 300sd, michigan road

Question
I am interested in purchasing a 1983 mercedes 240d from a friend of mine.  The car is in great condition except for the clutch, which will need to be replaced shortly.  No other problems exist, with starting, stalling, etc. but the car also has 225000 miles.  Will I be throwing my money away if I buy this car?  How long can mercedes go for before dying?  And how expensive is it to fix this type of vehicle should anything else go wrong?  Thank you.

Answer
My 1985 300SD had 250K miles when I bought it, have had it three years + roughly 75K miles.
I plan for it to last 450K miles or more, but Michigan road salt may impact body life.

I know people with 240D that have 750K miles and higher.

If you ignore maintenance and drive hard all the time; expect it to be junk in less than two years.