Well I found 20 mins to have a tinker with it this morning, just after the sun came up, news is, I am pretty sure not good
Removed MC and eventually with a lot of scraping got the piston out, to find this:
and this:
Which in my mind looks scrap, this is after attempting a bit of a clean with some plastic brillo type stuff. The bore looks fine further down, but the top where the end of the piston goes is rather nastily ridged, not longitudinal scores, but rings of rust, if you see what I mean.... Notice the lovely colour of the brake fluid -there was a fine powdery rust int eh bottom of the reservoir!
Seal kit is out I reckon, now looking for a replacement which doesn't cost the £225 from LR, or come in a blue box for £40!
For those that haven't see the insides of the MC before, here they are, nothing rocket science about it, the small bit comes down from the top and holds the larger piston in the bore, and stops it falling out. Other more simple MCs often use a circlip to hold the piston in IME.