I would venture to say that you could probably cobble up some kind of replacement section, to fill in that missing section. It could be held in place with some 1/4 inch bolts nuts and flat and lock washers, with the threaded part of the bolt on the outside! Doesn't look too tough a job. If ya live near Pittsburgh, Pa., let me know. I have a mower just like that one. It is an orphan, because it just wanderred in one day, unannounced, and decided to stay, receiving some TLC!

Yes, I would say the missing piece is the root of your problem. The blade and deck are not actually discharging the clumps. What is happening is, the gap in the skirt is performing like a discharge chute. The discharged clippings are thrown out of the gap before being mulched. They build up and fall from the driving axle components directly behind that gap. That is where your clumps are from Like rustyj said, you could make something that would restore the integrity of the mulching baffle. Nobody would ever see the repair unless you turned the machine upside down and showed them. You could fabricate a replacement repair section out of a short pieces of vinyl bordering strips (edging strips).

OK, I have some vinyl siding. Maybe try that, double it up.

Thanks!

In answer to part two of your question, if you have had it for ten years and put 200 hours on it and this is the only issue, yeah, it's a pretty good mower. It looks to still be in great shape and well worth keeping.