Am another who has had no problems with the Jabsco toilets over many years.
Seems to be a small number of users who have the various problems described - I put it down to (in the main because there can be duds of any product when it comes from assembly) failure to read or follow the instructions with the maintenance
kits (RTFM!), "ham fistedness" when doing the 6 valve cover screws up (and as MarkJ points out, not doing them up evenly as is good engineering practice) and using the wrong maintenance kit (that despite the very clear instructions on the package label as to which is which of the two types).
Is only a 5 minute job to completely service
one of these toilets and very clean as the piston and cylinder are self cleaning
and all the valving (except the joker) are on the clean water
side (unlike the Lavacs, for example - keep your hair on Lavac
owners, I am not criticising them just using them as an example
Anyone who claims other toilets are by nature problem free have experience limited to just their own singular lucky use with those others - I have seen them all with issues. Those issues can cost as much or more to fix as a whole replacement Jabsco .
What I have found is good for lubricating the piston is the silicon based runny, slimy lubricant used by plumbers/fitters for sliding rubber ring seals
onto large diameter pipes - here it can be bought in big tubes and a squirt of that after lifting the valve cover seems to work well and is no danger
to the seals
and o'rings. If the stickiness comes back a few days after a dose of that then it is generally that the O'ring needs replacing.