The fact that there was an issue with the grid leak is of no surprise. Those have an attrition rate as many were of a poor design. The bullet type that looked more the shape of a Festoon globe often had a cartridge that was extremely unreliable.

It would come as no surprise that it failed & someone had no idea how to fix it. However, always a good thing to follow procedures and end up not killing something. Resisting exuberance and not jumping in both feet, can have its rewards. Always pays to have circuit to check it against, prior to even thinking about powering: The Monkeys do strange and amazing things (normally wrongly).

If you can get the caps of of those bullet grid leaks off, and clear out the rubbish, you can use 1/8 Watt in there. I normally drill a one mm hole in the caps solder one reassemble and use as little time & heat soldering the other cap, as is possible. Tinning the cap before assembly helps.

For interest with a UX-201-A as a detector Average use Grid leak, 2-5Meg; Weak signal 5-9 Meg. But if the circuit says 3Meg so be it.

Marc