Hey there, klr250. Good to have ya. Make yourself at home.
About that fuel tap...... just to make sure we are on the same page here, are we talking about the fuel supply valve at the bottom of the tank, leading to the carburetor? In some circles, that would be referred to as the "petcock". And if that be the item in question, I may have an option for you.
Throw it away.
Really. There is an option available to replace this component with. It is from the enemy camp, Yamaha.
See part #11 / 23F-24500-11-00 / FUEL COCK ASSY
This is a bolt on modification, requiring no special tools or skills.
Your current petcock / fuel cock assy / fuel tap has two lines leading from it....one to the carburetor, the other is a vacuum supply line, the vacuum line the smaller in diameter of the two. The vacuum supply line will need to be plugged with a bolt or cap of some sort. The bike will then be "gravity fed" fuel, as apposed to the factory "vacuum fed" set up. Less parts, less chance of vacuum failure, less chance of leakage and / or walking. Anyone who believes vacuum assist is an enhancement isn't old enough to recall vacuum powered windshield wipers on cars.
I claim little hands on experience with the KLR 250, however, we just had a new member sign on who is intimately familiar with the workings and idiosyncrasies of your bike. If he doesn't see this thread, try PM'ing member Damocles.
Again, welcome to the forum.
EDIT: I have discovered that our member klr250 is located in the London, England area. I cannot help with parts procurement there. The parts I suggested are from any Yamaha TW200. Hopefully, these parts would be available at a local dealership. Good luck on your search.