Thanks, Jock.
From the diving sites I've checked, they all say that a diver needs perfect ET function or they shouldn't be diving...
Have a look at
This Link
At the bottom of the item, it talks about Laser Eustachian tuboplasty, which appears to be an interesting option. Try Google.
Here's a couple of links I found:
http://www.ncbi.nlm.nih.gov/pubmed/12671411
http://www.ncbi.nlm.nih.gov/pubmed/14724483
CONCLUSION: Laser eustachian tuboplasty is a new procedure that has demonstrated early promise in correcting intractable eustachian tube dysfunction with few complications. Further studies will be necessary to reproduce the results and establish the role of laser eustachian tuboplasty in the management of chronic intractable eustachian tube dysfunction