It's pretty common for the bolts holding the Extension Housing to break off in the transmission case..
You're near the ocean so that doesn't help..I don't know what's worse driving on salty winter roads, or being near the salty ocean..
Either way the salt will oxidize the bolt threads, and make it difficult to remove the fastener..
The last time I had to remove a broken bolt that was supposed to hold the Extension Housing on..I used Cobalt drill bits..
Basically starting with a smaller bit, and progressively moving up in size..Then I used a tap to thread the hole once it was drilled out large enough..
I was able to use all of the stock size fasteners by doing it this way..
If you ever have to drill out a grade 8 bolt I suggest starting with tungsten carbide..The cobalt drill bits tend to walk more in the grade 8 material..
In hindsight I should have used grade 8 studs, and 12 point nuts to reattach the Extension Housing..
With the studs all you're removing is a nut..That's easier to deal with than a steel
bolt in an aluminum