The early Mercedes engines used a plug in the real oil passage holes similar to the ones on the front of the block. Why could'nt you tap the holes on the rear and use a threaded plug like the early cars had? This would insure you that the ball would not come out. You would not have any oil leak there.I have never had to remove them when I rebuild an engine.I tell the machine shop to clean the engine with the front facing down. If you want to remove them,the manual says to use a long rod and knock them out from the front. Good luck.
Bill Lewallen Lex.Ky.