Michael,
You posted on FB about tubes...I don't have a FB account, so I'll reply here. I lost one 18x5.5 tube spontaneously last year.
The 18x5.5 isn't as rare as you've heard. It's on TBMs, King Air 200s, Beech 99s, Dash 8's, and the Lear 20 series...
https://www.goodyearaviation.com/sea...urnformat=json