Very sorry to hear dude this is truly terrible
I agree with Sank on the valves, since from what I have read the OEM valves are some of the only things that HPF do not replace if the go for 1000bhp since they are apparently good for up to 1500bhp or something so it is very strange that one of them should have failed.
As to the rest of the valves showing some real wear and tear this is quite strange as well, how many km's did the car do since the engine was built by G&C? I'm not trying to blame anyone, just looking for answers if anyone is wondering. I just think that this must have happened recently since G&C would probably have said replace if they were in the same condition when the engine was built.
If like you said the build can cost up to R50k I would be very hesitant to pay that amount and I would rather look for a replacement engine, I'm just saying you have options don't forget.
If you need anything else or whatever don't hesitate to shout the Fanatics family is there for a reason :thumbs: