Heck, I used to use the parts washer in my shop when I was a mechanic. It worked great on everything, unfortunately, that included parkerizing. Didn't hurt blueing or stainless (of course), but parkerized, and you had an expensive mistake. Thankfully the gun came back from being blued very nice.
As to PB Blaster, I've never used it on firearms, but I've used it on any number of other things and I feel it's far superior to WD 40.