Gap seals

Now that my radio is working again my attention is turning back towards glider performance. My PIK 20B has very close fitting ailerons, but no mylar seals on them. My question is, are gap seals required top and bottom, just bottom, just top? I think the laminar flow is off the wing by the time it gets back to the ailerons on top?

Udo Rumpf said The Pik20 and the LS3 use both the FX67-15%&17%

The Performance can be enhanced by first: making the airfoil accurate in both shape plus or minus 2.5% and waves within the .002"-.004" tolerance and second installing a turbulator on the top at about 52% chord. I would use 3/16" cylinder dots about .040" high and spaced 1.25" apart. Within 1.5" down stream due to the 35 deg. wake the "top" surface will be awash in turbulent attach flow, at higher speed the effect will take a little more distance..

So what is the proper way to measure 52% chord?

Thanks,
3Y