yep i've got this problem as well with my valver, happens when i go round corners a bit fast, doesn't stay on too long once the car straightens up, maybe 5 secs. Also i was starting to get some horrible noises from the head (nothing too bad, but not a good look)
Have already done a flush and oil change (carlube) and although it seems to have solved the head noise problems the oil light (and f**kin annoying buzzer) is now coming on a little more than before (and now not only after going round a corner, balls).
Have also had the advice to check the pick up in the sump but am now concerned before i start this that i don't want to fook up the sealing of the sump when i replace it, never about seizing the engine. Will have to look at that quite seriously when i do it.
Also another MK2 owner i know has installed a oil pressure guage so that he can monitor the actual pressure and not rely on the (sometimes dodgy) oil pressure warning sensor.
So basically i'm going to do the sump check (as i have already bought the gasket), then if not fixed will do the oil pressure guage i reckon as i don't fancy doing the oil pump if not required innit.
Will let you know how i get on when i do it, also if you manage to solve it please let me know what your solution was.