Yeah, After considering the facts, I did deburr the cocking slot. It just can't be that a H135 needs burrs to function properly, although Hatsans have pretty astounding technical solutions, like the one-side-only pivot joint shim. Maybe some people take off an unnecessarily large amount of metal when deburring, and Ellingsworth was warning against that. I find the job tedious enough to go with a bare minimum, a test of which is inserting the piston without marring the piston seal.
My 135 had stringy tar applied to the mainspring by the seller, who installed the spring. It was obviously put there the smooth out the shot cycle, which it did - for the first 300 shots or so. Logically, by that time the tar had been shaken to bits, and had no effect, outside maybe cutting the MV some.Reading up on the H135 here, an old post by Paul68 had the same reasoning as to why tarring is only a very temporary solution with these supermagnums. I'm going to turn a custom Delrin spring guide and tophat for the gun, with steel washers taking the brunt of the spring. That ought to do wonders for the 135.