From what you have described, you may have only fixed part of the problem by replacing the fuel shut-off. The gunk in the lines needs to be cleaned out or it will continue to cause problems.
I went through some of this on mine. The PO had the valve replaced but the "mechanic" didn't clean the system. All it will take is time and 1-2 cans of brake cleaner. Also, the oil causes the flex fittings to deteriate and causes them to leak. (about $10 replaces them all)
Remember it is a vacuum
system. Changing one failed part won't necessarily cure the whole system.
