Gooey belt from panny rx-cs780

I got a rx-cs780, and the fast forward/rewind worked, but the play was broken. I opened it up, a smaller belt was broken into 2 pieces. It wasn't brittle as I would expect, but gooey and left my finger and anything it touched black. I pressed it against a piece of white paper and it stuck. I'm going to get a sbm6.5 to replace it, but is it common for belts to degrade into a gooey mess?

Yep. And it leaves a mess. And if you don't get rid of all hints of it, it will get all over everything. If it gets on the floor, you will track it all over the house, and they are buggers to remove. If it gets on your favorite shirt or pants, they are likely permanently stained.

I replaced the belt, and now the play function works. I'm surprised about how good this box sounds; even the cassette sounds really good. The radio level is a bit higher than the aux or tape, but still fine. For some reason the auto-stop on the fast forward and rewind don't work. I can hear the motor still spinning inside. Any ideas why that is?

missing belt, sbm6.5 connects from the bottom right black pulley to the upper left yellowish pulley. I'm not sure what the black pulley on the lower left is for.