OK, so...
Things just improved significantly with my GTI :-)
All the "problems" that were being reported by numerous flashy lights on my clocks (oil pressure warning, check engine warning, brakes warning, coolant warning, PAS warning..) were all fixed in one fell swoop with a can of WD40 and a screwdriver.
On a hunch, I took the clocks off and sprayed the plug with some contact fluid, gave it all a good clean and plugged it back in. Started it up, and.....
All is cherry. No warning lights, car is perfectly happy.
thank smeg for that!!!! I have since apologized to the car profusely for cursing it and calling all sorts of unrepeatable names.
We are now friends... and it's actually a charming little thing to drive, now that I'm used to the way it drives. My last car was a Porsche Boxster (1999 2.5 litre) - and as I'm sure you can imagine, the Mk3 Golf GTI feels a little...different!
I've decided not to treat the car just as a runaround, but instead to embark on a restoration project and get it as good as I can. Some of you have done some amazing things with their Mk3s - I'm going to be looking around for inspiration on what to tackle first! I think to be honest it's going to need to be the suspension. I just don't like how it's so soft on corners, so that's gotta be changed :-)
Here's hoping I won't need to cry for help too often in this forum, but the support I got from you all this time was wicked, many thanks!