Planer "skips" when planing (irregularly) can leave mark on stock when happens.

Note:
I'd ensure each problem is fixed before you delve deeper, though understand consolidating part order. Ensure planer unplugged, blah, blah, blah. steps 1-3 are ok for novice, step 4 intermediate/difficult

1. Check feed rollers if show significant wear, replace will need to follow chain and bushing steps below. If glazed clean with solvent (alcohol or thinner using scrub pad). Don't cut yourself on blades
2. Check rubber (nylon) drive belt (located right side from front)
remove top 4 allen bolts
remove allen securing height adjuster, then remove handle assembly
remove 4 screws holding left and right plastic side panels
lift out side panels
inspect belt if shows any wear, replace
3. Check drive chains (located left side from front, FYI chains do have normal slack, no tension adj)
remove plastic chain cover, 2 screws on bottom front/back
remove snap rings
ease out sprockets front/rear to remove chains
check chains, make sure all links flex easily, if any bind replace chain
inspect sprockets, any damage replace
4.Inspect bushings (securing screws are a bitch to get out, can try ratchet w/ phillips, I had to use vice grips on heads when phillips started to strip)
raise cutterhead all the way
Start with 2 rear bushings
2 screws secure each bushing retaining bracket, FYI there are springs pushing down on bushings, but not heavily loaded, ease both out a few turns at a time. watch bushing, should move downward with spring pressure easily. If it binds bushing and/or spring may need replacement
same deal with front
when reinstalling, ease screws in back/front a bit at a time
5. Drive gears (now we're getting into more difficulty, proceed at you own risk. may have missed some screws, but if you're game for attempting this, you'll get the jist)
Remove top cover (black) of planer.
Remove dust chute (3 phillips) and rear blade access cover (2 allen)
Remove 4 allen screws underneath front of motor assembly
Remove power switch (6 phillips), disconnect leads (label to ensure proper reattachment)
Remove nylon belt shroud (rt side, 1 phillips), take belt off rollers
remove power cord securing screw (left side, 1 phillips)
Lift out motor assembly
Remove 2 screws left side securing plastic housing, remove housing
detach ground lead (green wire, 1 phillips)
Remove 4 screws securing gearcase cover, remove carefully
Inspect all gears replace if damaged. Note: if smallest drive gear damaged is actually the end of armature. big money part...plus bearings, etc...

Put everything back together

This is what I found:
drive rollers worn but I decided not to replace yet
nylon drive belt was original, looked ok but had discolored to almost brown so I replaced
1 drive chain (inner) had bad link
bushing on left rear (drive side) had been a bit mangled/cracked either causing or caused by skipping, so I replaced both rear bushings
armature spiral drive gear showed wear but big $ part, plus bearings..etc.... older planer so no replacement for me
everything else looked fine

I fixed the problems in order as listed but still skipped. Not until I got into gearcase (with no replacements) and reassembled did skipping stop, but no obvious problems...

Have planed quite a bit since with no probs, running like new-

....disassemble..reassemble..disassemble...I've heard patience is a virtue, hours spent, good luck