I am going to take the rocker cover off this weekend to check that the cylinder head bolts are correctly torqued as the head gasket was done recently.
As the gasket was new will I need to put a new one on or just clean up the existing one and re-fit it?

They will have been angle tightened in three stages if done right, torque , angle, angle. Can't see how you could check unless one is loose or you open them off and start from scratch. Then you're into how many times have they been stretched. Are they new? Twice ok three at a pinch.
You should be able to reuse the gasket, just get a pea sized blob of sealer where it starts to go over the hump.

I just want to check they are all tight Brendan. I did pay for new bolts so I have to assume so.
Do you think it's a waste of time?

Right now yes. Try the Forte trick for a bit. As I recall your compression numbers were reasonable. If they weren't tightened I would expect coolant loss, poor compression and possibly stuff making it's way to the outside of the gasket. Sometimes waiting is the better option.
If I had done the head I would definitely check - head like a sieve at times
Anyway if I suspected a job was done badly I wouldn't touch it, just bring it back and these head bolts do not need the tighten up after 500 miles kind of thing.

OK thanks. Forte it is for now!
Not sure what you meant with your last bit - do the head bolts need re-tightening anyway (even on a job that's been done right)? I saw somewhere that they should but I don't think Mr Haynes mentions it in his manuals.

No re-tightening. The only way I could see them being loose is they weren't tightened in the first place or they have been stretched too many times.The book says once only. Our own is a two timer.