I get a leak from my bathtub but only when the drain’s clogged. Before I pay a bunch to get it inspected, can I get any ideas? Thank you.
Put the stopper in and fill the tub. Check the stopper is actually watertight.
If it leaks, then the leak is above the stopper. If it leaks only when water reaches the overflow, then it's the overflow. Otherwise, it's the joint around the drain hole on the inside of the tub (red arrow).
If it doesn't leak with the stopper in, but leaks when the drain is clogged, then the leak is between the drain hole and the place where it clogs, so that's probably one of the joints (blue arrows). The most likely culprit is the joint between the drain assembly and the tub.
If the thing is accessible, it isn't difficult to fix.
For example if the screw that holds the drain assembly against the tub is not tightened, then the joints will not be watertight, and it will leak at the place where the tub contacts the drain assembly. You can grab the thing from below and wiggle it, see if it stays in place or if it is loose.