Yes the LH carb is almost always the leaker when on the side stand. Even with working petcocks, the RH carb lets air in the lines, while the LH is busy drooling fuel 'til all the fuel in the lines has drained. This can happen even with good float valves, My guess; after shut off engine heat evaporates fuel from the float bowls, enough that both float valves will open slightly setting up the slow fuel line drain down.
Viton tipped float needle experiment coming soon, to a set of BS38's living here.
Viton tipped float needle experiment coming soon, to a set of BS38's living here.