A book could be written on this subject.  There are so many points to
cover.  Concerning additives: there is no single super-duper cure-all.
Nothing works well every time.  In fact, sometimes what works for a
while ends up being detrimental in the long run.

When I find a stiff action, I go by my previous experience and often
start with what worked the last time I faced the problem.  I usually
begin with dry-cleaning fluid, the safe stuff, to clean out the felt
as well as possible.  Then I might try Protek, a thin lubricant that
sometimes works very well.  I have not found it to do harm in any use.
It is expensive, though.

I have never found center pin lube to do what it is supposed to.
Perhaps there is a good formula available somewhere.  I haven't seen
one, though.  Alcohol and water works well on new bushings to size the
felt.  In desperation, I've tried LPS (a thin lubricant), naphtha and
silicone mixture, and once I tried a soldering iron touched to the pin
to heat and shrink the felt.

I've also heard of one guy who used lighter fluid.  Apparently it
worked.  Ultimately, it may come down to repinning, replacing the
bushing, or replacing the parts.  Good luck.

Jeff Davis in Seattle, WA