When it's jamming, it is already quite worn. I wished I had been told to watch that at about same frequency you watch chain slack.I fitted a grease nipple to mine, should be a factory item.
Not too many people will even try that grease nipple/fitting mod. But greasing the shift lever very much overlooked and it is terribly annoying (perhaps even risky) when the shifting no longer works! It's only going to get worse with bike age. So grease now and often to avoid wear.
I did that mod today.
Summary: (you need a few tools I'm not going to enumerate, make inventory and plan while you read!)
a) take the whole peg bracket assembly off. It's easy and a lot more comfortable to work that on the bench. The peg nut is 34 N.m torque, which is not that easy to undo with the little allen key which is the only thing that fits between bolt and muffler. The bracket is held by 3x 6mm allen bolts (25N.m) which you will find behind the frame cover. Leave the shifter adjustment rod alone, just unbolt the grooved shifter shaft clamp (10mm bolt to remove completely). Note the little punched alignment dots already on the shaft and it's clamp. You can make that easier to read by drawing a tin line with a felt pen across the shaft and clamp cleaned surface.
b) If you made the mistake of putting 'red' thread locker the last time you reassembled, like I did, you will need heat (and a lighter or small butane torch will not heat fast enough; I used a propane torch). Don't overheat because there are 2 seals and you don't want to melt them. Although these seals are a joke, I'd rather keep them. That peg bolt spec is at 34 Nm, so you would be advised to set a torque wrench to 36-38Nm perhaps (?) while trying to unscrew, to avoid breaking the bolt.
c) you will find a groove all around the peg shaft not quite in the middle. that where I measure the grease fitting should be above. It would spread the grease around the shaft before spreading it sideways. It's almost designed for that! The thickness of the cylinder of the shift lever is slightly less than 1/4". So the grease nipple/fitting threaded part will not protrude inside and there is not cutting or grinding required, assuming you bought the smallest 1/4" dia fitting.
d) while in the vise (use some non marking vise jaws or piece of woods to clamp the lever by the flat ends of the cylinder) punch a pilot mark pretty much opposite of the shifter rod or a bit downward if you prefer. Drill patiently the steel with a 1/8" first, aiming straight perpendicular in the core of course. Then drill with 7/32" for final hole.
e) tap with a 1/4" thread 28 (but please double check the parts you bought - there can be metric and sae ones..). You should REALLY practice somewhere else if you have never tapped before... This is not time for error.
f) with a dremmel grinding ball (if you ever wondered where a spherical grinder could ever be used, that's it) or at worse a round file, remove the hanging shards around the aperture you made in the core that the drilling/tapping may have pushed in. Be very careful to only file those, not the cylinder faces.
g) cleanup, screw the grease fitting tight. Test if you'd like, or grease by hand for this time during re-assembly.
h) if your shifter seems loose sideways, particularly with age, it's normal wear. I inserted a manually cut-to-fit thin but hard plastic disk (not the soft plastic from ice cream contain but more like those pre-made meals container that you would send to microwave) to act like a washer, on the peg side of the cylinder. Test that it isn't too thick and that the shifter is still free. This is not likely to last forever (although the grease should help) but it's will take the wear instead of the costly parts.
i) use blue thread locker at most on the 34 Nm peg bolt. Re-assemble everything. Don't rinse, don't repeat.