The ethnicity aspect of DNA tests is not really scientific and just for fun as much as anything else. All "5% Germanic Europe" means is that there is a small element of your DNA that most closely matches people who are in Ancestry's database that either live in "Germanic Europe" (where ever that is and as defined by Ancestry) or who think their ancestors come from there. These samples probably only relate to people who lived during the last hundred years, and when you think of the upheavals in Europe over the last century, those people could have come from anywhere over that time. There are lots of threads on Rootschat that explain this much better than I have.
What you now need to do is to try to track down shared DNA matches and try to eliminate those whose ancestry you can work out - what's left may be descendants of your mystery gt gt gt grandfather. They should not be closer to you than 4th cousins and will only share a small amount of DNA (20 or 30 cms at the most, I think). Kaybron's reply (reply no 1) gives lots of useful suggestions. Good luck!
