I really like my w124 250d wagon the best. speaking of bulletproof...

haven't opened the valve covers yet, someone told me it could be the tensioner that has lost hydraulic pressure or the oil pump screen that could be blocked. The oil pressure does go up when starting the car, but rather slow? It did sit for 20 years... Are those reasons for a sloppy chain maybe?
how hard is it to take off oil pan, is the center support in the way?