The 2008 55 ATA have a reputation for being unreliable and is often targeted as the start of the end for Marzocchi. Some forks were definitely problematic, but some were also pretty good, my personal experience was that my own fork was trouble free and 100% reliable.
As intended the 55 ATA, was light, stiff and offered a lot of adjustment. Each cartridge was hugely technical, the micro Ti damper was closed to save weight and offered a strong lock style feature. The ATA cartridge offered not only a positive and negative spring, but adjustable ramp up (PAR) way ahead of the competition, plus 40mm external on the dial travel adjust. if all of this sounds good, here are some of the things to look out for.
Plug units undo: Add Loctite and tighten to 20Nm
ATA Internal failure: the main issue was the PAR piston that is tethered by a small cord, if this chamber isn't inflated first the cord could get twisted or caught on the piston causing air failure. The correct set up was to charge the PAR first to set the deck height of that piston, then charge the main chamber (actually this is the same as a modern Ohlins).There was also an updated O-ring kit for the cartridge to help prevent air transfer, part 8501267/C
ATA excessive noise: notable during riding you could hear a rattle coming from the top of the ATA. Solution, add thick grease to the ATA threads.
ATA wind down: Early forks could self travel adjust where the twisting motion of the work when riding would just spin the ATA travel adjust feature loosing fork travel. The fix was a redesigned top cap feature notches that would index with the top plugs cassette pattern.
ATA ultimate fix: Was the coil conversion, detailed here.
Bushing issues: The bushing tolerance varied somewhat and was generally excessive. The fix was an update to the bushings with a knurled texture on the back, with tightened the tolerance.
Axle: The ratcheting axle would fail leaving the lever to just spin, the later axle solved the problem and was backwards compatible to this model.
