$2.99 "expand-tite" piece, 1-1/4" to 1-3/8" as pictures. Was a very snug fit before tightening down, now it is not going anywhere, ever. Solid rubber block that expands when the bolt thru it is tightened, should work beautifully. Just thought some others may be interested

 

 

A little black touch up and that is perfect.

 

Have to be careful using that kind of plug in that plastic tube, it could expand enough to split the plastic and may stretch it over time even if it doesn't split it.

 

Fair point, different materials and the plastic isn't particularly flexible. I tend to keep a close eye on everything under the hood, so will see how this holds up