HELP on which engine oil ?

[87320i]

I have recently purchased a mint 320i - its an original mrk 1, 2 door coupe with 1 previous lady ower and f/s/h, its only done 60k!! it could be a classic, but basiclly im new to cars and dont know where to look.
Can anyone help me on which engine oil to use?? ive heard a lot about synthetic oils, but want get it right before i put any in.
The main light on the dash isn't on but the one on the obc is - showing engine oil ??

Any help with this would be appreciated...

details of the car:-
320i 2 door coupe, 1987 with an m20 engine

[Simon]

Have a look at the sticky thread at the top of the tech section!