Probably not too many others out there with the ancient HS2, Panasonics first HDD DVDR dating back to '02
While I don't have a HS2 I do have several other 10+ year old HDD Panasonics and I can say that several have a sticky DVD tray. What I usually do is if I push EJECT and only hear a humming, I immediately manually open the flap covering the DVD tray opening. Next I use my fingers to grab DVD tray and gently pull. Thats always worked for me, as soon as I start to pull the tray it opens, if the tray sticks in the open position I simply gradually push the tray in at which point it sucks it back in by itself.
I'm guessing a belt or idler pulley is shiny, giving it less grip to automatically open the tray. As pulling/pushing the tray has always worked for me, I haven't torn it apart to see if it could be serviced but I suppose it's possible your belt or idler pulley has broken, in which case replacement may be your only option.
If your not a DIY type of person you might send mickinct a PM, he's AVS's resident Panasonic repair person and should be able to take care of you.