Well. Friday didn't go so well due to circumstances beyond my control, so I couldn't take it for its MOT.
Good news is that the cam belt is fine. Once the cover was off and we'd rocked it back and forth in gear, the belt looks fine. Changed the oil (old oil was like treacle) and filter. New washer bottle slotted straight in. Wiper motor issue is probabaly a bad earth, so that should be easy enough. The spark plugs that were in it were fine too.
New rubber arrived but no time to fit, got the seats out but no time to get the driver's seat frame welded up, and no time to change the gearbox oil either.
Bad news is the new headlight units I bought don't fit (tabs on the new units look completely different to the tabs on the originals - any tips?).
Then we started to investigate why it was seeping oil out of the top of the engine. It wasn't a lot so I'd assumed that the cam cover gaskets had gone. However, airbox etc removed we discovered that one cam housing cover bolt would not tighten. Removed to discover this:

The threaded section of the cam housing has broken away, which is why the cam housing cover won't tighten. Very lucky indeed that the bit that had broken off hadn't fallen into the cams and engine, or it'd be toast!
So now I either have to try and source another cam housing, or try and find a good aluminium welder to weld it up, heat treat it, and retap the thread.
I've used some instant gasket and araldited around the head of the bolt to the cam cover, so the car drives still, but I don't really want to drive it far until I can get it fixed properly. I'm trying to remind myself that it is lucky I found the problem before it got much more serious and terminal.