I have fourteen year old 9 speed Shimano 6510 shifters (with Flightdeck) on my road bike and the right shifter is playing up.
Only occurs when shifting down rather than clicking up the gears and is intermittent, where the shifter just flops about and does not pull the cable. Faffing with the shifter while riding brings it back to life and it is fine for a while!
Replacement shifter or something more simple?

Cheers

fourteen year old 9 speed Shimano 6510 shiftersand the right shifter is playing up and the right shifter is worn out.

Mine did that.

I found some NOS that had different flight deck buttons, but I managed to move the controls from the old to the new. All still working fine.

If you work out how to fix them I’d be very interested as I’ve still got the old ones (in amongst all my other old crap…)

Yup, it’s worn out.

Spray a bit of wd40 in there . Worked for me in th past.