Often times you'll here people on here (and everywhere else for that mater) say that you should buy the brand of saw that has good dealer support in your area. This is a prime example of why MOST of the time, that's absolutely terrible advice. A few years ago, I started having problems with an 036. It was late fall, and I was busy hunting, butchering, and cutting firewood, and didn't have time to mess with it. I took it to a local dealer to diagnose the issue. They said the piston and cylinder were shot, and it wasn't worth fixing the saw. I took it home and checked the compression. It was 150 psi which was EXACTLY what the compression was 9 years earlier when I bought the saw used. I slapped a new spark plug in it, and it ran like a champ. Their $350 estimate ended up costing me less than $10. I've had similar experiences at almost every dealership within an hour of my house. Dealerships have a minimum quota of saws they are required to sell every year in order to maintain their dealership, and that quote often goes up every year. Thus their focus is on selling new saws, not fixing old ones, and they can't afford to pay a good repair tech $50K a year so they can afford to raise a family.
As far as your saw goes, yes rebuild it. 140psi isn't great, but it's not terrible. Go to the chainsaw section on this forum and start asking questions. If you need a saw soon, decide whether you want something bigger or smaller than your 359 and go buy that. We will all agree that its' never a bad thing to have an extra saw or two (dozen), but realistically having a 2nd saw IS a good idea. Its useful when you get a bar pinched, but it's even more useful when you have a problem like this and one of your saws is down. With the crap fuel that we have today, this is always a possibility. Really sucks driving out to the woods to cut some firewood only to find out that your saw won't start....