If it has 2100 electronics my guess is the spa is from around 2003.
The company I work for sold Cal Spas from 2005-2009, but I am not in the service end of it. Where exactly is it leaking from in the diverter valve? Is it underneath where the plumbing glues into it? I have seen a lot of Cal Spas that are approximately 10 years old where a glue joint starts leaking and it's almost as if the glue fails and the two pieces of pvc come apart. If not there, then either there has to be a bad o-ring or the cap that screws onto the valve is broken/cracked and as soon as the pump turns on and there is pressure it starts to leak.
As for the "OH", is pump 1 running and pushing water? If there is not adequate water flow through the heater, the water in the heat boils and gets over the 110 degrees and that is why it will "OH" even if the water in the spa is not warm. When you say the control panel is bad, can you turn the pumps on and adjust the temperature? If you can turn the pumps on/off and adjust the temp, probably not a bad control panel. Electronics were about the most reliable thing on those older Cal Spas. As BullFrongSpasMN said, the ozone is likely either dead or producing no ozone.
