Since everyone was so responsive on my previous thread on Amsoil Vs. Mobil 1, I'd like to ask another question regarding oil for my old cars. I am fortunate enough to have 5 other vehicles than my daily driver 300M, as follows: '68 Chrysler 300 440 V8, 79K miles, gets driven maybe 300 miles a year if that currently '68 Newport Custom with a 383 2 bbl. that gets driven the most, maybe 6000 miles a year. '68 New Yorker with a 440, 79K miles, just bought it and it needs an oil change. '70 Fury III convertible with a 440, engine is nearly dead, replacement 440 going in this Summer. '70 Fury Custom Suburban station wagon, was 383 2 bbl, now 383 4 bbl. Thermoquad, maybe gets driven 200 miles a year currently until I can redo the front end. I have been using Valvoline Maxlife regular Dino oil in 20W50 in all of the above cars. I noticed it really cleaned the engines (except for the convertible engine which is a sluge pile). I also use a 51515 Wix filter. I guess my question involves the oil I am using and the change interval. Am I using the right oil or am I better of saving some money and switching to Shell Rotella 15W40 that I can buy in 5 gallon drums at Costco? Other than oil selection, how often should I change the oil on all of the above given the limited driving that some of them get? Thanks in advance for responses!