Finally! After years of trying, I got local reception of Radio Northern Star here in the USA. I'd been trying again the past few weeks around my local sunset for greyline reception, once we got into the dead of winter, but had no luck getting audio, just a carrier.
Apparently the trick was trying for greyline in the middle of the night, around sunrise in Europe. Sure enough, I had a usable signal, weak for sure, but there it was. And even kindly confirmed by station operator Svenn after I sent him several audio recordings.