See if a clutch drum is available that takes rim sprockets. The rims are MUCH cheaper than the combination clutch drum/spur sprocket, AND much easier to change once installed.
While you have the bar off, clean out the whole groove to the bottom, and inspect the rail surfaces where the chain rides.
The rails should be even/not worn and perpendicular to the sides of the bar. Also look for a ridge that forms from wear on the rail edges. You can touch up the rails by draw filing with a flat file, or buying a tool made to do that.
When you have the bar off to clean the bar/under the chain cover, flip the bar when reinstalling so it the chain rides/wears on both rails evenly.
That bars rails need to be dressed. Post some pictures of the rails.
Do you have vice and a large flat file to dress it?
You can make a groove cleaning tool with a LARGE long steel nail/spike. With a large hammer peen the tip flat enough to fit into the groove, then grind/file a hook into the flattened tip. Put the nail in a vice and put a bend a little above the flattened tip, in the same plane as the flattened tip. If this is not clear let me know and I can take a picture of the tool.
