New radiators leaking from valve stem?

I've installed some new Kudox radiators and where the valve stem (or is it a valve tail - whatever, the bit that connects the valve to the radiator) enters the radiator there are leaks in 3 of the radiators. Not constant, just a small drip here and there. I've wrapped the threads in PTFE tape. Is it simply a case that I need to add more tape? I have filled the system and currently have flush solution going around, and will be draining that in the next few days to then refill the system with clean water with inhibitor. Should I fix the leaks at that point (draining down the system) or do it now while the cleaning solution is still in?