240D blues ...

[revphil1]

Hello out there,
I have a 1981 240D which I bought for $900 a year ago - the mileage says 53,000 although who knows if it's correct? Since then, a lot of things failed on it. I replaced the alternator, the transmission, the muffler. Then the engine blew. At this point I paused for thought and to catch my breath. My question: If I replace the engine, what else may I reasonably expect will go wrong with it? Am I "over the hump" already, having put about $3000 in so far? Can anyone recommend the preventive maintenance I should perform to make it a reliable vehicle?
Much appreciation, this is hopefully only the first phase of my owning this thing.
My goal is to run it on vegetable oil!
But I'll sell it now and cut my losses if it's just gonna be a MONEY PIT!
Please advise!