I didn't think so while I was markering the model... I did the same thing with a micro version of the deltie without any adverse effect, In fact I've gotten outstanding flight times from the micro. 3 minutes plus in still air!!!
but on a standard deltie I markered the vertical stabs and center spar.. it never got good flight times, an untouched (other than small Nar number) of the same model for the same sheet of balsa.. fly's fine.. It's TRUELY a mystery to me... but Robert had his Deltie thunder that flew the same afternoon perfectly...I think I'd go with the stain if you want...I'm going to do something to mine when I rebuild.. Just not all that marker...I really did go a little overboard
I just can't imagine that was the problem.. NO other reasoning was given by the way after the crash.. just "NOT do that on the replacement"! Guess their ment to be flown naked