Oil filter/pressure relief valve

[Hugo]

Another one of my silly questions - I was just cleaning the oil filter housing with a stiff paintbrush ready to refit it, & what I assume to be the pressure relief valve fell out & hid itself behind the steel backing plate. Having popped the steel plate off I can see where it was staked in place - the stakes are still prominent but don't seem to have done a lot of good.
Is it safe for me to just stick it back in & re-stake it? Or is it likely to do the same thing on the road? I'm tempted to stick it back in with POR 15 - that sticks like nothing I've ever seen (I used it to stick my core plugs in also).
The manual shows a completely different pressure relief valve arrangement (even on the Series II example). The book helpfully tells me that I will find the oil filter on the right side of the engine, but nothing more.
Now for the silly bit - I removed a screw-in plug from behind the filter housing to make sure everything was clean behind it, but I now find there are two possible holes for it to go back in (in fact there always were two!), & I'm not sure which hole it came out of.
Any ideas?