There are quite a lot of posts that describe how to fix the Canada balsam problem.
But I couldn't find anything related (or useful) to modern Epoxy / UV glue, and too bad, I got some of those lens on hand, so ... lets do something.

What I got is Rodenstock Apo Rodagon 300/5.6 Enlarger len, both front and rear element has the len separation problems.

Lens in water, and ready for heat up.

I heated it up until it boil, and then cool down for 10 mins, you can see the rainbow get larger!