A straight 30 W will be fine, be careful with higher viscosity oils though, many run them in older motors to get better oil pressure, and as their clearances have opened up enough to drop oil pressure in the recommended oil viscosity, they are fine doing so.
Because it’s higher viscosity it can also help reduce consumption.
However just as with everything else there are drawbacks, the drawback is that thicker oil will reduce flow, thats how it raises pressure, but reduced flow reduces cooling
For some reasons people get upset and want to argue with me when I tell then that piston engines are oil cooled, they say no they are not, they are water
cooled cause that’s what they have been told. The cylinder heads and to some extent the cylinder themselves are water
cooled, but every other moving part it’s the oil that does the cooling
, camshaft, crankshaft and all the bearings heat is carried away by the oil.
Reduce the oil flow and you reduce the cooling.
In warmer weather
you will be fine with 40W, just don’t be tempted to think a little is good, more must be better and start running even thicker oil.
I don’t think it’s your valve stems myself. Valve stems seals getting hard and wearing results in very little oil consumption, the biggest indicator of valve stem seal wear is it will smoke like a train when first started, then the smoke begins to dissipate as its burned off. Worn valve stem seals will allow oil to leak into the cylinder, that’s why one with bad seals will smoke so bad at start up, but as it’s a tiny leak it stops smoking soon after.
If running her hard for a period has much if any effect, it’s rings not seated well, and hopefully the running hard will seat them. If it has no effect, it’s not rings. I have never seen a bore so glazed that running hard had no effect, I have seen a few that it helped but the only fix was to hone the cylinders. A polished bore running hard won’t have much effect, the only fix is a hone.
Both glazing and polishing can be seen with a bore scope
though if it’s a DI motor and you can get into the cylinder, if it’s an IDI I don’t think you can.
Excessive blow caused by polishing or glazing is bad because it increases ring and cylinder wear, soots up the oil bad, and cause excessive oil temps.