I would suggest that yes the cone is designed to seat in a receiver housing to direct grease from the grease gun through the relief valve and into the tensioner assembly. It also provides a seal. The primary seal, though, (to prevent back flow of grease and excessive pressure on the zerk fitting) is from a check ball relief valve inside the body of the fitting. I believe a zerk fitting can handle somewhere between 3k to 6k psi. That said, an excavator bouncing around on the tracks and tensioner assembly likely create even greater peak pressures. This would literally blow the zerk out of its housing if a relief valve or check ball valve inside the fitting didn't stop it. All of that said, worn or damaged housing threads (cone likely won't seat properly), damaged fitting threads, worn out zerk, and worn or improperly fitting cone end of the fitting into the housing are all potential leakage points. I believe the design purpose for fittings with two rows of threads with a channel in between or one row of threads with channels on both sides is so that removal isn't dangerous and prevents pressurized grease from blowing in the direction of the operator. I haven't seen this on an excavator but on servicing harvesting and cannery machinery. The two rows of threads act as a pressure safety release. If the threads didn't hold anything then this wouldn’t be in the design. So, a faulty track adjuster valve (I believe this one has a spring ball valve inserted inside the body of the fitting) can fail on several levels: the coned end doesn't seat properly, the ball valve near the cone inside the fitting has debris, is worn, or fails, and the back-up zerk ball valve/spring can't handle the pressure or is worn, the fitting itself wasn't properly tightened and is loose, worn or housing/fitting threads are damaged. Yes, I believe grease can leak around the threads in certain conditions. Best, Allan