The Montello SLX came out in 1985 and was Pinarello's top of the line bike. I would imagine that this bike is worth a lot of money, depending on the year, size and whether it had S-Record or Record components. This is easily worth 4 figures. Don't let him mess it up. While I recall seeing some on Ebay in the past, I couldn't find any that came up on a search of completed auctions, so they are obviously in short supply.
The decals are peeling on all old Pinarellos unless they have been replaced. That shouldn't really effect its value that much.
If it is a 60cm frame, don't tell me. My wife would kill me if I bought that bike.