Oil light on at idle when warm.

Don't just throw heavy oil at it—not unless/until you're sure it's due to worn bearings. Other posters here are right: use a mechanical pressure gauge to find out what the oil pressure actually is at hot idle. If you don't want to go to the hassle, replacing the sender's a good bet; they tend to get lazy with age and can cry "wolf". And inspect the sender wire; if it grounds out anywhere along its length, the light'll go on.

That said, it will also be a good idea to service the oil pressure relief valve to make sure it's doing its job, as described in these two threads: thread 1, thread 2. If that valve sticks partway open, it'll drop your oil pressure.