I can vouch for the E60 525i. Solid car, I’ve never had any really bad problems with mine.
In the ~7 years I’ve owned mine (bought at 8 years old with 150k miles on the clock), I’ve had to:
- replace the front springs
- replace the front shocks
- replace an ignition coil
- have a wiring repair job done on the reversing switch
… and other than that, it’s been fuel, filters, and tyres. It’s been solidly reliable, decently fun to drive, and very practical.
I think this says it all.
Running an engine with no lubrication is not going to be good for it. And now you’ve put oil in it and it isn’t driving very well, then that tells me some very bad things have happened inside.
You’re looking at a big bill for repair.