I'm gonna chime in here on a couple of items as I also have the same saw but it's newer and no issues 'cause I treat mine to a proper oil mix and have from the get go....
First off, any Echo dealer with beans should have the drive sprocket clutch assembly because in reality it's a 'consumable item' and I believe Saw it again has them in stock or at least they did last time I checked.
Echo has what I consider to be a sneaky approach to Cat's in the muffler. Mine had one when I bought it and by the way, a new piston and jug won't come close to what the saw retails for. I actually replaced the muffler on mine before I even started it the first time and I replaced it with the OEM non cat muffler, I'd give you the part number but I tossed the box it came in, but rest assured, if there is a circular cat in the muffler (you can see it if you remove the top baffle plate easily), if no cat forget about the above...
I also modified the top baffle plate, I removed entirely the under plate that Echo installs, for whatever reason I'm not sure about, but it's gone now. Did the same deal on my Timber bear as well.
Far as sealing the air cleaner to the carb throat, get yourself an '0' ring to fit the throat firmly and add a smaller '0' ring to the back side of the filter housing, issue of ingress of fines, solved.
Probably take some 'slack' for this comment but, if you replace the piston and jug (and in my humble opinion, you need to replace both, start the saw out (first couple tanks on 40:1. not the 50:1 and use Echo Red Armor 2 stroke oil and not Stihl or some off brand. I run all my saws on Red Armor and when I inspect the exhaust ports and mufflers (I'm anal about carbon buildup, always have been actually because carbon in the exhaust port and muffler entrance robs power), with Red Armor I get NO carbon at all. Now, because I run mine infrequently, I do use the Echo Red Armor canned (50-1) fuel but that is me and I don't use them every day either.
They seem to take at least 3 tanks of pre-mix or canned fuel to develop good power. Had a Stihl professional top handle arborists saw and when I first got mine, it felt like it was down a bit on suds but that has vanished now the saw has been run a bit. Don't ask what happened to the Stihl top handle except to say, I ran it over with my truck and that was the end of a 700 buck saw.
Far as the bar goes, I'd take a good look at the rails as well inner track. You can buy genuine Echo bars for your saw on Amazon as well as replacement loops pretty cheap (I'm not a big fan of Amazon but they are there).
Compared to my flattened Stihl, I feel that once the saw had some time on it, it is comparable to the Stihl top handle now and you'll go through the same 'break in' if you replace the piston and jug. Just make sure you properly torque the hold down bolts and use an inch pound torque wrench as 'good-n-tight' don't work well.
I like mine just fine and now that it has some hours on it, quite satisfied with it, especially when considering the cost of the Echo was just about half what the Stihl cost me.
Like I stated, I'm not a professional arborist, just a farm owner with a huge woodlot that needs taken care of.
Finally, on chains, I grind all my own chains. I own 2 chain grinders, I really only need one but I sharpen chipper knives for all the local arborists and I also grind their chains now that the cost of chains has kept pace with inflation so I need 2 grinders, one to grind the cutters and the other to set the rakers and on the subject of what I refer to as the 'ghost raker' on the low kickback loops, I drop them when I set the normal rakers, usually at least 0.030. That eliminates the 'chatter' effect that was mentioned in a previous post.
It's a good saw in my humble opinion and yours was at some point either run lean or not enough oil added to the fuel. If the blanking plugs are intact on the carb screws, I'd say a bad batch of pre mix was used. If not, the previous owner was fooling with the mixture screws. Echo likes to set their saws from the factory, slightly rich for some reason. I've never fiddled with either of mine as I can deal with a tad bit of 4 stroking when pedal to the metal and that vanishes once the saw is in the wood and pulling a cutting chain anyway.
Just my 2 cents for what it's worth, take it or leave it, I'm good with that.
