X Fusion O2 shock rebuild.

My Whyte JW4 has a linkage front suspension therefore it has 2 very similar X Fusion O2 shock absorbers. The ride was never the quietest but had become intolerable even after I replaced the loose shock mounting hardware. I had clearly lost a lot of the damping which was allowing both shocks to extend with a noisy clatter over rough ground. I was also finding that over technical rocky bits the front was out of control due to seriously reduced damping.
I was quoted £95 to rebuild each shock. Way too much for my taste.
My only option was to do the job myself. I knew I couldn't pressurise the damper with nitrogen but I'd heard that this is not a big issue.
I've found the necessary seals online but since I didn't have any air leaking I thought I'd have a look inside and see what it looked like.
With the bottom mounts removed I depressurised and clamped the top mount in a vice to unscrew the air can. Easy enough. Inside it all looked immaculate. The damper is held in by a screw in cap which can be removed with a 19mm spanner.
As I pulled the plunger out it was obvious what the problem was. The oil didn't seem to have leaked but it was about the viscosity of water and pinky beige in colour. I tipped it out and cleaned everything up. I couldn't find any online info about the oil volume so here's what to do.
Push the damper piston all the way down through the seal. Fill the reservoir with fork oil (10W grade) to the bottom of the threads and push the piston into it, wiping away anything which comes out. Screw the cap in. I had to pull the top up a bit to get the spanner on it and I then tightened up. Pushing the piston right down again I then undid the nitrogen reservoir screw. I then extended the shock to it's full length an tightened the screw back in filling the reservoir with air (80% nitrogen!).
I lubed well with PURE MTB grease and put the air can back on. I pumped up to my chosen pressure (140 psi) and refitted the shock (front in this case). A quick test and it's like brand new.
Tomorrow I'll do the rear shock in the same way and take it for a blast. Quietly.

Job's a guddun! I've just finished the rear shock and it feels perfect and perfectly quiet. The oil was the right sort of colour this time but a little depleted after 14 years and very thin. I've given the rear spokes half a turn each but just think the flexibility is my fault for buying a cheap wheel.
Checking it over also had me tightening the bolts on those pesky rear suspension linkages, which were allowing a bit of flex.
If you do consider opening your shock, particularly if you open the damper cartridge, just be careful and scrupulously clean. It's not a hard job but unknown territory is always a worry. As with most MTB work you should never need brute strength.

Good job mate - I "whimped out" have switched to RP23's front and rear and what transformation that was - my 02 was just blowing through its travel - the only thing I have had to get used to is that they are back to front compared to each other so the propedal levers must allways be opposite !

Also I have now got a diy front shock guard made from landrover inner wheel arch liner!

My PRST 4 has Fox shocks and they are much quieter. I did a lap of a local red graded circuit in 11 mins 12 seconds. 19 seconds quicker than on my Boardman FS Pro. It's the climbing ability, of course, not the downhilling that does it.

To me the frame is too short to do that so I use it to walk my dog and we go over a few hills and I dont have a dropper on mine so I only go up to 20mph down hill rough with him. and I wont use it on long rides or with the clubs i am in as I think i am too tall for it. so its less stable for me on longer fast rides