Hello Vanagon Types

I am doing some rust abatement currently focusing on the engine carrier bar.  The bar ends are badly rusted but the bar itself is solid.  I tried pulling out the end caps, but they are corroded into place.  Before I apply more force I thought I would ask this group about the caps and thoughts on protecting the bar itself.  I did a quick check online and apparently the end caps are no longer available.  Assuming I cannot get them out without destroying them, does anyone know what they are made of, how they are attached, and if there are any alternatives?  Are they just rubber caps pushed into place?   It appears they have no function beyond keeping the bar closed to outside moisture, so anything that covers the bar end would work as well?

Thanks in advance
Dave B
Boise