Quick backround:
Country home, so we have a well, shallow well.  Water was being pumped via a surface pump (aka jet pump, centrifugal (sp) pump).  Any how, low water last year (irrigation) and what ever, dropped the well level.... resulted in lower level.... pump could not 'lift' water.  End result, kept running and impeller went.....

Okay, so we put a new subersible pump in and new storage tank (old one gonner). System is set w/ a 30/50 pressure switch.  Old system had very little air in tank, not enought to read on tire guage.  New tank set to 28psi air, 2lbs less then low cut off.

Okay, one faucet in the house leaks water, but never did before.... and it's hot water.  Okay, so I change the little 'rubbers' (springs reused since wrong kit purchased, but springs are springs, right...oh the kit had stright type springs.  Original were tapered, bigger top then bottom. Delta kitchen type single facent, but used in laundry room).  Old ones looked worn.  Changed the rubber that goes on the ball (new ball too, plastic). Well, this solves it for some time..... but tonight, no matter where you put the lever, it keeps on leaking!!  Aside from changing the ball to brass..... I'm at a loss.  The rubbers inside look good, seated well..... could it be the springs????

Kaliburz,

Went through this here awhile back. Kit wife bought had 2 sizes of rubbers and tapered springs. Before it was all over I tried both sizes of rubbers and new springs. Turned out that the ones I used were slightly longer than the originals and the post-mortem showed that they were mashed down and ground off at the end. In this case I put the wrong ones in first - needed the shorter ones. Then I had to replace the ball (from plastic back to metal) that switches on-off and hot to cold. I think you need the tapered springs and probably new rubber seals if it is still leaking.

Another thing you might do is flush the line out good before changing the seals. With mine I get some pipe scale and sand that is probably abrading the seals over time.

NMSight