Have talked with different useers of Royal Purple Synthetic Motor Oil who swear by its cleaning effects.
Really the manufactuor of the oil claims to drain about 1500 miles the first time in because it has cleaned it so well filter restriction is possible.
It even goes as far as to say on the bottle itself it cleans it internally. So the answer to your first asked question, according to RP is yes.
Most all of NAPA auto stores around the country are suppose to carry it, but can't verify for sure, only what I've been told. Cost is in the 4 to 5.50 range.
1989 420SEL 105575 miles
1990 Chevrolet E-Cab C-1500
1989 Olds Toranado Trofeo'