Its also worthwhile to lap the relief valve to the seat with some fine valve grinding paste. A piece of dowelling in the valve and away you go. I usually do this at every engine rebuild and don't normally have any idle oil pressure problems. But 25 psi at idle is fine.
If the valve is worn then the seat is probably worn as well. The seat can be replaced as it is a separate piece pressed into the oil gallery. Some times the seat falls out and other times it needs to be persuaded to come out.

Hope this helps
RonR

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68 build Mk1 Cooper S
72 Clubman GT project. Total restoration required

The relief valve seat in automatics has a 3/8 UNC thread in it. You can get these out easy with a head stud, a nut + washer and some spacers.
However most manual seats do not have a thread in, last time I had to remove one it needed a thread cut in it first. I checked my other 4 manual blocks and they were all like this.

If the seat is dodgy, a 9/16" steel ball will seal it better than the plunger does.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I think we will stick to the current setup in the engine then. We have a 9/16 ball with a good spring giving us 75 psi running hot with 25psi at idle hot

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- '74 Clubman Ute project