3/16 rigid fish tank tubing made a good repair if anyone else runs across this issue.

I have not. I'm trying to get 3/16 steel brake line to work right now, but I'm still having the issue of the wheels falling out as the wheel hubs are square and the brake line is obviously round on the in side. The size is great it's just a square peg in a round hole type of situation.

I have a few ho gs4s, all of them are relatively old. The plastic sleeves that hold the wheels together are cracking and are not holding the wheels very well if at all. I can't seem to find any replacements online anywhere. Where can I find these if they exist? Or what can I use in lieu of the plastic sleeves. Thanks.