This is unconfirmed information, just a guess
I know its 15 yrs old, and spending money on a saw that age can be money wasted,
but time is all it would take to tear it down, open the case and replace the seals and
bearings, and check the rings for wear, put new ring in if needed and piston is ok,
that would be the cheapest regarding getting it up and running, otherwise its a new saw
at a lot more money.
If money is an issue, then even more so get the old one fixed up before any air leak
destroys it.
Those 215 carbs seem very expensive, the original 215 has gone up in price a lot.
Hopefully you can clean the old carb put a kit in it and it will work, but you will
never know unless your sure there is no air leak, if there is one then even the 215
will not run correctly, you could put a carb off 660 on it and if the case is leaking
it still won't pull in fuel.