I've owned this house for about 4 years now, and am 2 to 3 years away from
selling it (not due to this problem).

In the master bathroom there is a small, either plastic or fiberglass tube.
It appears to be one of those liners but I have no idea. It looks, and feels
cheap when you step into it (I don't take baths, just showers). About 6
months after moving in I noticed the caulk around the seam between the tub
and the tiled walls was cracking and separating. I took out the old caulk
and recaulked the entire tub. A few month later, same thing. Noticed that
the right hand corner is where the flexing starts and is most pronounced.
Maybe 1/8th of an inch at the time. It's been about 3 or 4 times total that
I've recaulked this tub now.

I just did a search on this and I wish I had come to the internet before -
as the trick is to fill the tub with water first before caulking. However my
concern now is not just slight flex, but major flexing. I'm worried that the
foundation that the tub sits on is not right, as now the crack seems wider -
about 1/4" at it's widest point (starting at the same spot - right corner,
next to the piping/valves).

My worry is that I need to rip this tub out and repair what is below it. Is
this true? If so, how? Obviously I'd have to break the rest of the caulk
seem, but then what? I can't afford to have a pro do this.

Perhaps I should just fill the tub with water and try re-caulking and see if
that holds? It's *possible* that the crack is just bigger because I've let
it go without recaulking for a while, which I regret because this is a 2nd
floor bathroom and one morning I let water splash into that corner and it
leaked down into the ceiling. There is a slight, small water mark there now.

Help!