AZTallRider's questions about saddle tilt are right on the money. Sliding forward on a saddle is almost always caused by the nose being tilt down too much. I'd start with the saddle as level as possible, and I'd raise the seat post back where it was. After a 30+ year layoff you must also anticipate that your backside needs some time to acclimate. If you want to play with fore aft adjustments, I'd encourage you to only do that after you've got the seat level and back up where it was with another ride or two set up this way. I'm a believer in only changing one thing at a time. This way you know which change has caused what you're experiencing. If you go to fore and aft adjustments on the seat, I'd only go a half cm or 1/4 inch at a time. And, I'd probably go back 1/4 inch first. If that didn't do it, I'd go forward form that spot 1/2 inch. This should let you know if fore or aft is the direction you want to play with some more.