MV8

Third vote for a standard barb push on for rubber.

I looked at a 420r watts kit and see they use long shanks with minimal threading which is good. However, it could be the bolt shank is not threaded far enough to clamp the inner sleeve. It may be from tight build tolerances and/or a hardware mismatch. Washers generally are not made to a precise thickness. If you had a dial caliper you could measure the grip length and the sleeve length and compare. The bolt is just a clamp for the inner sleeve. If you don't have that then just add another washer with an id smaller than the step in the shank the washer causes the nut to stack tight further out and see how it goes. You should still have a few threads protruding above the nut.

Hello, I have no first hand experience with your model but I have a lot of experience and I also stayed at a Holiday Inn Express recently. There should be a steel sleeve within the bushing to act as a positive stop for the bolt and nut to clamp against. If the sleeve is there but too short, the added washers can help loosen the nut. Sometimes instead of a sleeve, a positive stop is provided by a shoulder on the bolt near where the threads end and the unthreaded shank begins. Either way, the sleeve or shank (step/shoulder to head) should be as long as the width of the bushes. With a step shank versus a sleeve, washers reduce the effective length of the shank. After that, jamb nuts, a new nyloc or other prevailing torque fastener such as a nord loc should work great! A pic of the hardware or exploded view of the assembly may shed more light.