I fix Discmans as a hobby, and in most cases this skipping, more pronounced at the end of a disk, means worn spindle motor. Since CD drives for CD50 were discontinued decades ago, you may try to reset CD platter onto a new Mabuchi motor.
Alternatively, if only some specific CDs skip, then you are in a good company of "post-VRDS" Wadia owners ;-) learn to live with this glitch... You may find this post (at square-2.com) interesting:
THE GOOD, THE BAD AND THE UGLY. CD PRESSING QUALITY
I give up with the link!!! here is the address:
http://square-2.com/the-good-the-bad-and-the-ugly-cd-pressing-quality/