My M26SS in my aftershock leaked all over when I got it. The fuel filter also leaked. The o-ring was pinched and torn at the factory. Needless to say, the first 2 tanks for break-in were two of the worst I've ever had.
After I got home and was thoroughly disgusted with the truck (brand new mind you) I was sitting there looking at it and realised there was fuel all over the filter, leaking out the backplate of the engine, out of the carb neck and out of the LSN.
Well, after tearing it down, cleaning all surfaces with DA, smearing RTV everywhere and putting associated green slime on the LSN o-ring, the remainder of break-in and the next 3 gallons were easy as pie. I also pulled the primer and sealed it up as well.
More prone to leaking than actually priming anyway.
The M26SS isn't a real powerhouse, but it gets the job done. I sold the engine for $40 after 2 or 3 gallons and the new owner has run another couple of gallons through it in his ebayed LST nightmare. It's one of his first engines and he runs it way harder than I would... and hotter.