^M1 0w-30 for 3,000 mile OCI for the next 3 oil changes should help a lot.
Also, instead of over-treating, he could begin with idle-flush additives just before dropping the used oil.
How about some fast runs on the interstate, too? Higher the RPM, the more work that area gets, right? That might encourage some of that crud to come off.
I don't see blotches and removing that stuff can sometimes spike wear, so I don't necessarily see the risk in 'blockage', perhaps some slowing of the oil return passages until it's suspended better. Oil-pick up, oil pump? Perhaps some debris, but more likely wear is going to happen without a complete attempt at manual cleaning. valve area, top-end, then oil pan removal, if you want to avoid circulating the crud that is insoluble, JMO...
M1 0w-40 is a good move, too, just perhaps 0w-30 for now and 0w-40 during the summer? ...but really any full synthetic will help. I like Amsoil, Ultra, Red Line...etc, they all have the goods as well. Buy in large containers at WM unless a special at a parts store is available.
PS: I'd compare the sound of the PCV valve to a new OE dealer PCV valve. Sometimes a new one will sound completely different from a used one. It'd be worth changing since it's so cheap anyway(usually, lol...dealers :[ ). The valve may still rattle, yet have a weakened internal spring(depending on the design).
Also, fuel additives with PEA, like Red Line SI-1 FSC from O'Reilly(most locations) claim to clean the PCV system as their vapors are strong enough to help with residual grime).