Speaking from experience I would almost certainly say that the oil will need replacing in the damper, which will mean new seals in the damper and this is something that will need know-how. Then there will either be the air spring which may be perfectly fine, so check it it holds the pressure. The sort of work required is a damper service and the telescope overhaul for the bearings/races to be cleaned, inspected and re-greased. I have four Cannondales, all with Headshoks so can guess what is needed. If you buy the castle tool and pin spanner you can take things appear to inspect but you really need to know when to stop because as you say the parts are discontinued and so a wrong move could render the fork dead if you don't strike lucky.
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That Eighty-Aid company look pretty expensive. Over here in the US we have a master mechanic in Mendon, NY that is a specialist and his work is fast, precise and extremely reasonable. I have the same fork on a 2001 Jekyll. I live in Hamburg.
The seals in the regular fatty DL70/80 set fit. You can also take seals from the hardware store for the air piston. They are a little smaller than the original seals, but the rubber tube is a little thicker, so it works.
The seals inside the oil damper are cannondale specific parts. Disassembling the needle bearing ist tricky, you need a good description and you have to build a tool that will hold the races in place, otherwise you will have problems to reasemble the fork.
(Don't mix the races). I twisted my air spring 180 degrees, because it lost air every 3-4 days.
Just removed the bottom plug and pressed it into to the other side. Now the fork is perfect since days. Just taken delivery of two FATTY folks and one MotoFR fork, all of which have been fully serviced.
That's new oil and seals for the dampers, clean inspect and re-lube races and bearings and all other necessary work you'd expect in a complete overhaul. The work is done by a Cannondale specialist that is well known in this forum. The price I paid for all three folks appears to be less than for one damper service at EightyAid.
Das ist nicht gut! In regards to the telescope dismantling. This would be a step requiring very very clear understanding of the task, special tools and skills. If you get those bearings or races out of the original location then things could go south quickly. Each bearing is precision placed and these vary by microns I believe. Mylo xyloto tour.
I pay less than $100 per fork and sleep well knowing the job is down correctly. Better than spending $100 on tools and wrecking you folks. Yes, the telescope dismantling is hard work, but you will find a manual for that at sheldon brown. The first time it took me two hours to rebuild the complete fork. The races are measured in microns, true. If you mix them up, because the fork falls into pieces during disassembly your screwed.
My problem was, that Dr. Cannondale told me that spare parts for my fork are discontinued, said, you can service all the seals, but not change the air spring, because the new ones don't fit. Besides: how long are the air cylinders of DL70 and DL80? Diameter must be the same than super fatty, bacause the seals fit.
My super fatty has and always had 65 mm travel, the removed oil cartridge has 70 mm travel, manual says it has 80 mm of travel, but thats advertising. Yes, the telescope dismantling is hard work, but you will find a manual for that at sheldon brown. The first time it took me two hours to rebuild the complete fork. The races are measured in microns, true. If you mix them up, because the fork falls into pieces during disassembly your screwed. My problem was, that Dr. Cannondale told me that spare parts for my fork are discontinued, said, you can service all the seals, but not change the air spring, because the new ones don't fit.
Besides: how long are the air cylinders of DL70 and DL80? Diameter must be the same than super fatty, bacause the seals fit. My super fatty has and always had 65 mm travel, the removed oil cartridge has 70 mm travel, manual says it has 80 mm of travel, but thats advertising. Bro, yes I reviewed Sheldon's info and I also found a very well documented procedure for MotoFR forks. Applause to you if you took it on and completed with success.