Never had anything other than perfect ballcups from Tamiya myself. As far as the hole-drilling for access goes, I tried it on a couple of cars in the past and now I don't bother. It takes lot of unpopping of ball ends before they wear dramatically, and drilling the hole is a lot of effort which just makes the cup more likely to stretch anyway.

The reason I started this post was a "funny story"... I was going to say how much this car continues to perplex me, as I went racing today expecting all sorts of problems with varying levels of grip on the track (started dry but a brief rain shower took the grip away before my second run), but I was surprised by how consistent it was during the day, with and without the centre screw on the top deck attached. It was pretty much perfect (by my standards) using kit settings with the exception of the springs and the fluids...

...and getting back home I just noticed that at some point during the day the bottom centre screw had fallen out of the car! So I have no idea what kind of chassis flex I was running.