Poor installation?

Smithy99

Abcdefghij

George_Michael

I would have thought that a leak due to poor workmanship would have become evident long before 17 months had passed.
It could be a small crack has appeared in the trap or the tray and may well have nothing to do with the  actual fitting.

Aylesbury_Duck

As above, could be a tiny crack or movement in the trap plumbing.  It's more likely to be a tiny gap in the seal around the tray.  I can't see how you have a case for poor work after 17 months.

Aylesbury_Duck

First thing first, you need to establish the reason for the leak.  That means calling the installer to check it if it's not something you're capable of doing.  It could be a number of things.  

Again, you're going to find it difficult to prove poor workmanship after so long and if the problem is parts-related, the onus is on you to prove an inherent manufacturing fault.