No experience with that type item but I do work on things that might be somewhat the same and I might throw in a really lowball idea for you to consider. Not necessarily recommended but a way to get by, perhaps?
I am involved in shipboard repairs at times and they have some of the same problems as RV. Lots of full time stress on things that a stationary unit don't have and that can make plastic develop stress cracks where things attach, even with the best tie downs and design. We have a saying about stuff happens?
So some of it is not practical to replace right then due to no parts, etc. and we make due until we can do better.
So some thoughts on how vital, how practical, and how important the item may be will lead you to a better decision. Is a low ball and maybe temporary fix, a practical idea or just not at all good, so that the $600 is a better move? Is the $600 for the part of 200 and $400 for labor to take it all apart again?
There are some wonderful sealers and some plastic can be melted back together. You know the loud mouth ads for "Flex-Seal" products? There are times when it is worth the try. If it is a less critical part, time important, and low labor cost, I might give it a shot to seal the old unit.
Decisions, Decisions? The work is easy but the decisions can kill you.