If it were me replacing the valve, i would elimanate the compression and us a solder on valve. i just think the only reason for the compression fitting is the original plumber is too lazy to solder the fittings. whe soldering a valve, i first remove the stem and seal to prevent possible heat damage to the rubber seal.

Just my opinion, and I am not SLAMMING plumbers, I just think compression fittings are a cheep fitting. (you will not fing them on aircraft :<)