Long time lurker, first time poster. Some incredible information on here!
I've finally gotten around to changing the brake fluid on my van and judging by the colour of the fluid coming out it was long overdue!
Anyway, when I got to the driver's side front brake I found that a previous owner or their mechanic had kindly completely rounded off the bleed valve.


I'd like to replace the valve but don't even know where to begin as regards the size of the valve or where to source one.
I didn't want to remove it in case I damaged it and was unable to put it back in well enough to seal the system again.
As far as I know they're the original callipers, they're definitely rusty enough to be 30 odd years old.

The only thing that makes me think they may not be original is that the bleed valve on the passenger side is 8mm and I've read that the originals are 7mm (the 2 rear brakes were 7mm). Or maybe someone's just replaced the valve at some stage.
Any advice would be greatly appreciated.
Cheers
1981 Air cooled T25, 2.0l petrol