I would take the car to someone who knows these engines problems etc.........probably your loacal MB dealer
when my engine failed I was afraid of a rebuild...especailly since MB only offered a 1 year warranty ......
I went with a completely rebuilt(by MB) long block assembly...not really a lot more than a rebuild and you get the peace of mind of a 48 month 50K MB parts and labor warranty
I Spoke with a gentleman the other day in PA who has a 1995 with 75K who experienced hammering at idle...and it was bad news.....he caught it early though and his oil consumption problems had not started as of yet...and MB is covering some of his fix
bottom line...take the car immediatly to have a compression and leakdown test
1992 300SD 120K