Delta Lahara T14238-SSLHD Shower Trim w/o Head Stainless

I had this (not sure if the same, mine says its a Monitor) installed in the walk-in shower last summer when we had a bathroom remodeled and I have had absolutely nothing but trouble ever since. It is not a consistent problem though and I have no idea what is happening. It won't cut off unless I take it apart and reset the springs and gasket. Then, it may last 20 minutes or two months. It will start spraying on it own with the handle in the off position. I have a pretty good analytical mind and I am stumped. I contacted Delta and while I was working things out with them, the thing began to perform just fine. It makes no sense. The way it is installed, access to the cutoff valves are in the kitchen and rather than go to the trouble of elaborating, it is an accident waiting to happen and part of a wall will have to be removed to change it. It has began to mess up again, and I think that its the gaskets and springs and not the cartridge itself. I read where people will buy a new unit, take out the new springs and gaskets and put the old ones in and then carry it back and exchange it. My wife remembered that the box had been opened on ours and this may very well be what has been the cause of our trouble. I don't mind buying new parts if it had worked for a reasonable period of time, but this thing has been trouble,off and on, for a year and a half. I am in the process of trying to contact Delta again. This may not actually be a problem that Delta is not responsible for, but it has their name on it, and a lifetime warranty with it.