Do a compression check and pull the muffler to check the piston and rings though the exhaust port for scoring. The exhaust side scores first do to heat. I had a Husqvarna 266 that I got once that had decent compression but the rings were welded to the piston and the piston was scored. I don't trust just a compression test alone.
If he compression looks good and you don't see scoring do a pressure/vacuum test. Again search the board to find out how. I on't trust old seals and I especially don't trust old seals that have sat idle for years.
If you have low compression or scoring you should rebuild the saw. If see scoring tear it down and check the damage. If you have aluminum transfer to the cylinder wall you can take it of it muriatic acid. Search this board to find out how. Go over it with 600 grit and oil after rinsing out the acid. Make sure it is perfectly clean before reassembly.
I bought a 028 Super that had been run on gas + ATF mix. It didn't work. The engine seized and I had to do what I described in this post. I bought parts through Northwood Saw for years and have been very happy. My 028 didn't cost much to rebuild. After I cleaned it up I found a low hour saw under the grease and grime so it looks like new. With new internals it runs like new too.
I replaced the piston and rings, carb boot, muffler gasket, impulse line, fuel line, carb kit, cylinder base gasket and fuel filter. Mine had a poorly repaired cracked handle that I replaced with a like-new used one I bought from eBay. I use my 028 for cutting firewood and although it is an old saw it is well made and will serve me for any years to come. They are worth rebuilding. If you don't want it I would love to have it.
Bob