I usually find the Seafoam at Murray's, I don't think autozone carries it. But you will actually pay the same price ($3.00 - $4.00) if you visit your local gm dealer and ask for GM Top engine cleaner (liquid) - they both work the same.
Your rear calipers may have been updated to the 1996 calipers by the previous owner. The orginal calipers are secured by a 18mm bolt, that you have to use a box wrench to tighten. How do you change your pads? If your calipers flip up on one end, you have the updated 96 calipers. If your caliper comes off as one assembly you have the originals.
I have a '92 Chevy Euro (3.4L), a '93 Cutlass Supreme (3.1L), & a '85 Lincoln Town Car Signature series. (my crusier)
Man! $30 bucks is a steal! I wish I had been so lucky.