Vaillant TurboMax Diverter Valve problem?

I'm sick of repairing this TurboMax. First, a history of problems.

The diverter valve, then a switch on the board, then the fan, now back at the diverter valve with lots of other problems developing along the way; e.g. the fill loop has been continually bleeding into the system due to a faulty fill tap, which kept it constantly at maximum pressure. When disconnected, pressure would fall over a week or two to nothing. The system drain valve was malfunctioning so I had to try draining it all through the radiators to repair it. Then the shutoff valve for the direct water had siezed shut (I'd snap it trying to open it) so I had to shutoff the water to the house and install a ball valve in the direct water line to replace the one in the boiler. Water was going everywhere in the meantime. There is a constant list of issues to fix with this thing, more than I've listed here, I hate it.

This time, I was getting the symptoms of diverter valve failure. Water out the taps but it's always cold, boiler doesn't ignite to heat tap water but it will run the radiators etc... Looking into the boiler, I found the microswitch on the valve wasn't operating. If I push it down with the tip of a screwdriver, the boiler would fire up to heat the tap water.

I stripped the diverter valve out and took it apart to replace the diaphragm. It was a bit messed up looking and there was a bit of limescale in there, but nothing serious, like a few grains of sand on the inside. Scrubbed it all clean, but it back together. On replacing the microswitch, I can see the valve stem is no longer tripping the switch when it moves. The tiny plastic arm with the brass bit on it, that goes between the stems and moves, pressing on the switch, has snapped. It's snapped right along the thinner section where the brass tip is, furthest from the switch.

There's no way I can glue that and expect it to last. I could try filing a replacement out of brass or plastic, but that'll be incredibly annoying. Is there a rebuild kit that would have one of these plastic arms in it? It doesn't come with the diaphragm kit but I thought there might be another with it.

Will have to buy a full diverter valve if not and those things, as with everything on the boiler, cost a fortune. Due to the constant fall in pressure and no signs of leaks, I also suspect something like the DHW may need replacing, which could mean a few hundred in total. At that point, having just replaced the fan for around 140, it makes me think it may be time for a new boiler.

Thanks!

John