There's two potential problems with the Philips mech used in the Marantz.
Skipping all over the disc is usually the result of a laser on its way out (which can be checked by looking at the RF waveform from the laser pickup, on a 'scope), skipping at specific locations, often in the Marantz on track 1 or 2 (check the time when it skips and see if it's consistent on the same disc) is often due to debris or old grease on the gears that drive the laser sled and more occasionally dried grease on the sled runners themselves.
Often examination will reveal some greasy bit of dust and fluff caught in a gear, and cleaning this will fix the problem - if the laser sled guides need lubricating clean them first then re-grease with a graphite-based lubricant.
To be honest it's easier to buy a new mech and fit it, as mentioned they are cheap.
Andy.