I thought i would share my little experience in changing the seals.
It's definitely not as hard as I thought initially.
So I first ordered this seal kit from VicaryPlants https://www.ebay.fr/itm/153238849986
As far as I'm concerned, all the big cylinders are the same on the 3c3.
The hardest part for me was removing the cap, first I had to make some kind of big wrench with a scrap piece turned on the lathe. I'm sure similar design could be made with a grinder and a welder. Then I added metal bars on the cap that my wrench could grab.
Then I had to attach the end of the rode to an anchor point and then slowly retract the boom (extendhoe). It could also be done with a tirfor or equivalent.
I thought I had to have a 58mm socket for the nut on the rode but it's not tight ! You just have to remove the pin.
I had a bit of a struggle only on one inner seal but not impossible if you twist it right.
Putting it together was straight forward. I made a mark on the cap before removing so that tightening torque wouldn't be a problem.
Longest part of the job was making the tool to remove the cap.
I think it's way worth doing.
Cheers