Older domestic, "wing nut" type tap leaks CO2 at the base when disconnected from keg. This is a unit I used to operate twenty years ago and am in the process of refurbishing. It's been so long, that I can't remember if this is normal or not.

I haven't tapped a keg yet so I don't know if the tap will leak when hooked to a keg. The rest of the system has pressured checked out OK. The lines are new, on both sides and everything has been cleaned and sterilized.
Will this tap likely leak when hooked to a keg, or can I just shut off the CO2 when changing kegs? Do I need a new tap or a rebuild or should I try it on a keg?
Thanks to everyone in advance. This is an awesome resource.