Kohler K-305 tub/shower faucet leaking hot water when closed

[rstephen]

I replaced the cartridge and pressure balancing unit (PBU) on a Kohler k-305 tub /shower faucet. The faucet now leaks hot water while turned off when a nearby faucet is running hot water. The original PBU GP500520 was replaced with the new "compatible" version GP800820.
The installation was very straight-forward so I am assuming either a bad part or the replacement PBU is not compatible. Any thoughts?

 

[Tuttles Revenge]

Maybe missing one of the sealing rings between the cartridge and PBU?

2nd Pic on the following link

https://www.us.kohler.com/us//productDetail/shower-valves/637956.htm?skuId=613402&brandId=empty&