If the "grease fix" got it deiseling like that, i bet the piston seal is frayed up. Probably needs to be cleaned up and deburred, and piston seal replace. At the price point, thats not a big deal. If you cleaned everything up real good with denatured alcohol and put a dab of ARH tar in the right places on reassembly, it will probably be better than new. Just grease, will work itself into the wrong places before you know it
With everything said and researched, I made a decision on what to do with my horribly dieseling (my fault) .177 Walther Terrus. I will be ordering the .22 version with synthetic stock and just replace the stock with my wood on the .177. The synthetic stock and rest of the .177 will go into the garbage unless someone wants it at a nominal price (plus shipping costs). Live and learn (life being a never ending learning curve) not to mess with a very nice and accurate gun myself. Thanks all for your input in this decision making process.