First off, observe/obey a very conservative OCI (4~6Kmiles typical). For some cars/engine designs, go with 4K
Second: unless it's a metered orifice type of PCV valving (Honda 7th gen civic 1.7L engine), otherwise, all checkvalve type PCV valve, simply toss it away and get a new one every 2 years, irregardless of mileage, and get a factory replacement (no aftermarket plse).
I personally would not care about keeping a PCV valve over an extended period of time unless I can assure myself that I'm providing a proper operational environment for it. And if you think by skimping on PCV valving replacement intervals, think again (esp. places where air-care/emissions testing are a must).
If you like to know what a good PCV valve should "sound", do this:
buy a new factory unit and keep it in the plastic bag. Take the old one off and then shake it and compared the sound of the one off your engine vs the one you bought. If you don't hear a clear, well-defined rattle or it takes too much effort to make it rattle then well, it's time to replace it.
and if these instructions aren't clear enough, might as well change the PCV valve on a regular basis and then forget about the rest.
As for engine sludge cleaning, AutoRx gets my vote. Most of the OTC cleaners we fould here are literally useless and frankly I don't waste my hard-earned $$ on it.