I have an echo model SRM 2501 trimmer. It has got to be at least 12 years old. Starts fine, runs fine year after year. However, it appears I have a got a leak coming from the muffler. I pulled off the muffler and entire insides are black and is wet with this black liquid. I quess gas/oil mix. Anyway, as the season goes on this liquid leaks out and runs down the unit eventually onto whatever its is sitting on. The exhaust port has alot of carbon built up. Could this be a problem as well? I hope this is not a dumb question but why is it leaking? Could it be a gasket of some kind or is not buring all the gas? Do I need to run a different gas oil ratio?