I have used Permatex MotoSeal on a few dozen rebuilds now, both with and without gaskets, and have had no leaking issues to this point. A friend who is a 2-stroke motorcycle nut gave me a partial tube when I did my first rebuild and I used it on his recommendation. It took several saws to use it up, and I am probably a little heavy handed on application. I think the last tube I bought came from Auto Zone, but I would imagine any auto parts store that carries Permatex products would have it. Its not very expensive and you do not use very much per saw.
I, and many others here have rebuilt several MS 290 frame size saws, if you need help / tools, ask.
Finally took the time to get the saw tore down tonight, must be the mildest straight gassing of all time. I got the rings out intact and there is only minimal transfer on the cylinder. think my cousin must be using 2/c oil from Borneo or something, piston head is crapola but cylinder head looks like it just came out of the box. Think I am gonna work on rings/piston with some 1200 grit, clean it up and see if I can reassemble it. Stay tuned! (These saws are a PITA to get apart and I probably did it wrong!)[/QUOTE]
I'm using up my tube of Dirko then I'll probably use Motoseal from now on...