Vern,
"Is that seal replaceable" Yes. the outside seal under what was the rag joint, is easy to change. (looks like a small wheelbearing seal) <under the keeper like nut.
it won't seal a major leak in the inner o-rings, it may need a rebuild.
There are Frame brace kits to help with a crack.
http://coloradok5.com/ordframebrace.shtml ^Source at the bottom of this link.
