RE: TBM 93
Yes the top part of the cylinder is threaded, so you just unscrew it, mine weren't that tight but use some grips if you need to.
The plumbers tape works really well, I have used it on two different sets of air retracts & has worked on both sets, can be a bit of a pain getting the head back in but lube it up with some vas and once in seals up nicely, I have had air still in my system two days after pumping them up !!.
Cheers.