I suspected that our 11 year old male cat has arthritis or some other
manner of joint problem (an x-ray performed a few months ago based on
nothing more than my hunch came back with my our vet saying it looks
like he might have some indication in one of his hips).  I'm not sure
if the x-ray showed the knees or not.

We've been feeding him some "CT Support Plus" once a day ever since
(Glucosamine, MSM, Multi-vitamin, minerals, etc).  It's a powder
that's easy to mix in with his food.

Anyways, not being old enough to know what arthritis feels like, we
have no idea if he has arthritis or how to go about getting a
definitive answer.  He's 18 lbs, very strong, but doesn't seem to want
to jump onto anything higher than himself.   Been that way for months,
maybe a year.  He seems generally grouchy when compared with a couple
years ago.  He is un-managable when taken to a vet (for his last exam,
when the x-rays were taken, he was put under with a seditive at our
recommendation and this will probably be standard practice every time
he goes in).

Basically, would it hurt to put him on any arthritis medication or
pain reliever even if he's not experiencing any pain?  (side question
- is aspirin bad for cats?)  In other words, treat him as if he has
some joint problem (arthritis, or rheumatism (?) or ... ?) and see if
he becomes more active or if his mood improves.

PS:  he does have a heart murmur (which if I'm not mistaken normally
leads to pulmonary hypertension) but his chest sounds are normal.  I'm
under the impression that the murmur is significant.  I'm thinking
that short of cardiac surgery there's really no treatment for this
(?).   I think I'll post this as a second question (since it's quite
different than the question about arthritis)...