I'm wondering if anyone can tell me when this rifle I'm looking at was manufactured? I'm assuming it was 1968, but I'm finding conflicting information on it. The Serial # starts with 68 94... Also, what should the rifle be cleaned with? I was told that PB Blast is good for moving parts.
Thanks in advance for any information you can give me...

A 68 is late 1968. Early 1968 models had the AD prefix, and were the last of the lettered serial numbers.

http://www.marlinowners.com/board/viewtopic.php?t=495

I have no experience with PB Blast. If you don't want to disassemble it, I'd remove the butt stock and flush it out with brake cleaner or WD-40. Then finish with Outers Tri-Lube or equivalent. Tube magazines are usually filthy, so take off the magazine end plug (watch the spring) and swab it out with a .410 shotgun cleaning rod. You may have to remove a barrel band screw to get the magazine follower out. If you spray lube the inside of the action, let it sit barrel up on some old newspaper overnight before you put the butt stock back on. That keeps the butt stock from getting soaked with surplus gun oil.

Bye
Jack