Hello,
I will be the LAST person to argue with Trev (since he always steers me straight, thank you), but I tried a different method. Specifically, using the old ball and some valve lapping compound to refinish the seat. I don't know yet if it worked, but I thought I had better try it having threatened to do so for some time.
In the first picture you see the ball epoxied on the end of a 1/4" aluminum tube. (this is the same tube I've used for timing, which is why it has the graticule with 1/32" increments). In the second picture, the tube is shown in my drill motor. I'm pretty sure the ball is smaller than 1/4" and I'll measure it later.
Richard L.
EDIT: 1/4" it is. Batting zero for February.