the tensioner needs oil to do its job... that could very well be it.
When I do an oil change, granted I drain the oil from the sump first, depending on how long the car has sat, either some oil will dribble out, or there will be none (just a small amount in the bottom of the cartridge holder).
Are you sure the level is correct? The M42 takes about 5.25 quarts, IIRC, I dnt have my manual in front of me.
The tensioner is a good place to start.. its right there on the right side of the car, just under the frontmost partof the right side of the valve cover (I hope thats a good enough explanation). Takes a 19mm socket IIRC.
Definitely worth changing if it hasnt been done in a long time. Might give you some insight into the cleanliness of the engine too... one problem with the M42 is that with the relatively big oil pan that has fins on it, and a relativlely small engine, the engine looses heat after shutdown quite fast... most tweaks to the heat can be seen on the temp gauge (unlike every other car I own). Doesntmake much of a difference, except that this car is more succeptible to condensation in the oil than a lot of others, IMO. My 318 is the only car that Ive ever gotten white traces of condensate on the dipstic when Ivve pulled it out in the cold part of winter. None of the other 8 cars do that ever.
JMH