TubeNet

I have had my Weimar small 4/4 CC (perhaps large 3/4 to some) for a couple of weeks now. All the pitches were pretty easy to drill down, either with common alternate fingerings or a little slide pulling / pushing. Except for the D above the staff. I have always played that note either open or first valve. Open - way out. First valve - way out. Pushed the slide all the way in - still much too far out to lip. Oh no, trouble. The D the octave below I can play either 1st pushed in or 4th, but I wouldn't dream of using the 4th valve above the staff. So, I start trying every possible combination. All of a sudden, 3rd valve - BINGO! Spot on in tune and slotted very easily. Been using that fingering it for a week now with no issues.
SO..., that got me thinking - has anyone with a G-50 with one of those "problem" high D's ever tried playing it just 3rd valve?

used to have that problem. I hated that note

I had a similar issue with my little Weril BBb. The C above the staff was very flat with open and with 1st valve. For a while I used 4th, which worked if my chops were in good shape. Then I found that 3rd valve was the answer, just as you did. Normally we do not use 3 alone because it is not tuned to a precise minor third. But sometimes the out-of tune nature of that valve tubing compensates for the out-of tune nature of a "problem" note; this is one such case.