Bubbles in the back of the lense

I bought a second hand Canon 85mm 1.2 two years ago. I noticed that I'm getting some bubbles in the rear element. I haven't notice anything in the images. I was going to take it into a shop to see what it would cost to have it fixed or should I even bother.
What is the cause of the bubbles, I have one trip in the Andes where we spend multiple days at high altitude.

I would expect that what you're seeing are a pair of lens elements separating, and air is getting into the cement. If the bubbles have always been there, they might be an original attribute of the lens - in which case it's probably not an issue with image quality..