Hot start problem resolved due to failed check valve in the DMCH fuel pump

[DMC5180]

This is where I get mine:
http://www.mcmaster.com/#metric-o-rings/=p3nifs

I use 1.9 mm X 3.8 mm but I think the stock size is 2.0 mm X 4.0 mm. Either works but I guess the smaller one gets more seal since it has less surface area. Viton is a little harder then Buna-N.

I fail to see how a smaller one gets MORE seal with LESS surface area.