Hiya mate, I know, you do what you can with what you have, ?
The brass pump heads with O, rings are very good, I do however prefer PTFE, I use it for Everything,
Machine Oversize, And leave it in the FREEZER !
When solid machine down to size, Works for Pump Heads ? pre-Charged Exhaust valves Etc, I use it on Most seals, Even Breech ! Etc, Cheers,,