Metal fly rod tubes are good protection, but eventually the O-rings get old, crack and fall off. Replacements O-rings are not generally expensive, but are typically a nuisance to find. Automotive versions are too small and the household applications only fit certain plumbing sizes. Hardware stores are stocked with various small fasteners, seals, and the like, but O-rings in right size and diameter are usually absent.
Finally, I found the O-rings I needed at Archies Hardware in Kernville. It is located on the Main Street and across the street from Sierra South and The Hut. I took my inventory of caps needing replacement and left with ten O-rings that seal the water out and keep the cap on.
Some of those fly rods have been neglected. Reminds me that I should do more fishing.....
Ants