I have see this buried in other threads by others but will post it here so it is searchable.
If you are going for a new petcock there are a couple of aftermarket a;alternatives. One is built for the Valk and has the vacuum control, the other is a direct interchange but is straight manual operated. You can use the OEM on/off/reserve handle and hardware. I put one of these on today and IMHO is the way to go.
The only difference is that the pickup tube is about 1/2" shorter and so you will get a bit more on main and a bit less of reserve.
The part number for the "manual" valve that I used is on one of the pics (18-4133). I am an Imgur virgin so once this is posted I'll check and see if I got the link to one pic or 2.
If you go to the K&L website you can see both models and there is a list of wholesalers that sell to the shops. The valve is available on EBay but only shows US sellers and so for me (Canada) it worked out better getting it from FortNine in Quebec and getting it mailed. They ship free after $50 and so I added a tube of moly paste and ended up paying the same for that as I would have for the now free shipping.
https://imgur.com/a/jr7m79rhttps://www.klsupply.com/carb-fuel/fuel-petcocks.asp