Interesting, I never use any ball stud from any of my STS engine(the ball stud still in the box) , the stock one from my cars (TTR S3 & Mugen MTX-4) seem to work perfactly. I wonder what car you have?
BTW, the mystery involve the pull start kept broken string on my D28M is solve, the problem is I was using a Ofna063 with a header that bend in the way that it touch teh pull start resulting a melt down. after I swap with a TTR pipe set. nothing have happend so far
STS is good engien with great value, LHS should carry them so people won't be scared away from this hobby the price tag of those Italian mill.