Special thanks to Michel Potheau for some of the information on this page.
Another great source of E12 info is the First Fives - E12 Registry, thanks to Gregory Szczyrbak. Big Coupe Group also has a lot of good info, early('76-'82) 6 series has many similar parts to the E12 5 series, brakes, suspension, electrical.
Check the differential mount. The original factory mount was not strong
enough and this usually breaks. It needs to be reinforced for it to last.
Motor mounts wear and tilt engine back. Eventually the brackets holding them will fatigue. Glance at the mounts, they will normally show a little compression at the back. If they show a lot, they are shot.
If you have trouble installing a new oilfilter, it's a sure sign the mounts
Speedo box (in line on cable) for oxy sensor mileage needs lube from time to