Thanks for the comments Whyhaveone.
Isn't it always the way that a simple scheduled maintenence turns into an exploration of possible upgrades?
So I do get your logic completely. Its about £140-180 to get someone else to service them (full disassembly and clean). That is just supply only, so i would have to remove and take them to Plymouth (25 miles) and collect them, refit them, which i can do, no problem. But that is a 100mile journey, plus the pennies they will want. All of that is without new parts, which would probably come to £50 or so. Note: i don't begrudge their mark up on parts, just being realistic!
The upgrade trick cartridges look good, and by all accounts are much better than stock valving.
But theres the rub- they are really expensive and well out of my budget.
I only use the bike for touring, so i cant really justify it. I am lucky that i can use my Z900RS for spirited, faster riding.
I am now thinking that i might as well do the whole thing myself. That way i can strip them right down and clean/inspect to my own satisfaction .However, i have never done this before and i think i will need one or two special tools.
A seal driver for sure, if i am intending to change the dust and oil seals.
I get your point about the head race bearings. No doubt, whilst i am in there i will inspect and re-pack with grease. If anyone has any advise on servicing forks, gratefully received.
I know that theres a couple of YT vids on it by Wrenchie and Delboy. I may also get the manual to help along the way.
Pyramid seals look like a good supplier and i am sure fleabay can deliver on the seal driver.
Many thanks again.