Splined crank interface question

[glepore]

I have a new to me stages left gxp arm (ebay purchase) that apparently has enough interface wear that even when fully tight it has a slight amount of play-enough that it has a clunk at the bottom of the pedal stroke. (know its the crank b/c I reinstalled the stock arm and issue disappears). I put a couple wraps of teflon tape around the splines which has cured the play in the workstand but wonder about the long term benefit.
Does anyone have real world experience with a fix? I'm thinking about cleaning the interface and using loctite bearing retainer. What say you folks?

[Mark McM]

If there is that much play, then you will likely need to replace the crank arm. The reason for the press-fit is because the left crank is subject to an alternating load - when you apply pedal drive force, you are applying a counter-clockwise torque on the crank interface, and if you ever stand on the pedals with the left crank pointing back, you're applying a clockwise torque on the crank interface. Without a tight press fit, there may be movement between the crank and spindle. And this alternating rotation can act to unscrew the crank bolt.

The teflon tape may have temporarily quieted the movement, but teflon likely isn't strong enough to withstand the forces and pressures it will experience.