There is no conflict of opinion on your fault.
But it is a job many professionals like to pass by.
There is no way that you will be able to manage to replace the diverter valve yourself. Unless you are superhuman!
Most replace the complete valve, but some only the diaphragm although that involves a lot of dismantling. If you have plenty of space underneath and some nice little tools it can be done in situ. But still not a very nice job.
But it is a job many professionals like to pass by.
There is no way that you will be able to manage to replace the diverter valve yourself. Unless you are superhuman!
Most replace the complete valve, but some only the diaphragm although that involves a lot of dismantling. If you have plenty of space underneath and some nice little tools it can be done in situ. But still not a very nice job.