[Chas]

Occasionally, repairs (soldering) to socket pins causes solder to flow in areas where it causes a mechanical obstruction..

Try inserting the tube, be sure key is aligned, from below while observing the socket from the underside. blades of the pins and the lock ring will all move slightly if as the tube is inserted. If a pin contact does not show movement then it is likely there is an obstruction.

I don't envy loctal socket replacement, it is difficult to find new sockets and an RF stage is usually crammed with critical components. You may have to re-align if there is a disturbance to the wiring...

YMMV

Chas