If you are asking me, I honestly would not clean them ever. I questioned the porosity when I saw the edge flake off of a layer around the screw holes instead of a chunk. At least that's how it looks in the pic. They are beautiful just the way they are. I wouldn't be afraid of them being on a limited use gun, but a shooter doesn't deserve those grips. Just me.
You can quick date any S&W revolver by looking at the barrel where it meets the frame or at the cylinder where the cartridge rim rests. 1982 was the last year for what is called "Pinned and Recessed". 1982 on they changed production techniques to speed up production. A Pinned & Recessed gun is easy to distinguish as the cylinder gap is very tight at the rear of the cylinder. Flip the cylinder out and each cartridge bore has a shoulder machined in the hammer end of the cylinder. When you drop a round in the head of the cartridge is flush with the surface of the cylinder. Pinned refers to indexing the barrel to the frame. It is a simple pin through the frame that engages the top of the barrel and locks it in place. Once you see a P & R gun compared to a non-P&R and newer you can spot it at 3 feet. You don't even have to pick it up. P & R guns are a little more desirable and a little pricier due to age. They don't shoot any better or worse, but they took far more effort to manufacture. I really like the fit and finish of a P & R gun. The newer guns just don't have the look... I own both and shoot the latter stuff but don't shoot the older stuff... Again, just me.
EDIT
I had to change the dates. I was going from memory and sadly it aint what it used to be. The 72-73 dates were when Bangor-Punta owned S&W. Sorry for any confusion. I have a S&W branded Bangor-Punta labeled model 41 (the model 4 is the S&W 22 automatic and a super little gun) .177 caliber air pistol in its original box. This also was when S&W sold Shotguns and bolt action rifles. They were all supplied by Mossberg.