Welcome to a fairly exclusive club of early GTi owners

. I too have one of the first RHD in the UK with only 79k on the clock and all original.
Hopefully your car is economical to repair, but the seats will be a nightmare to get hold of. Your right, they are a checked "tartan" pattern - red cars had red check, black and silver cars had black/silver tartan.
Do you still have the 1600 with 4 speed box too and what colour is it?
If you want any help give us a shout as I also have all the reference brochures, plus take a look at the pics of my car in my sig link.