Repaired bathtub gasket leak from 7 years ago leaks again

Seeking advice on leak problem caused (likely) by a faulty repair. PSA: overflow drain gaskets should be replaced periodically (every 5-10 years?), just as washing machine hoses should be.

We had a leak in 2018, called a plumber to address it and they siliconed the overfill gasket for our tub. Well, it has leaked again causing expensive repairs to the condo unit below. Not sure why they didn't replace the gasket in 2018- maybe the supplier didn't have it or something? But my belief is that the plumber who fixed it in 2018 might be responsible for damages. I believe that is why plumbers are ticketed, licensed, and insured, right? Or is it to make me feel that they are less likely to make mistakes??

Do we agree, and how do I proceed? I think this matter is too small for a lawyer (I've been told if damage were over $100k it might be worthwhile, but the repairs to the unit below are likely less than $5k) and I've contacted my insurance broker with details. I don't want my insurance rates to go up (again) so won't be making a claim.

I will be contacting the plumber who repaired it in 2018 and ask what my expectations should be as I want to be reasonable.

Will he offer to chip in for the Reno's or am I out to lunch