Its funny, I've been working with the Tektronix AM503 / A6302 setup some years ago, and my experience is that they are quite accurate.
A well maintained and calibrated AM503/A6302 will easily give you precision within the limits of your scopes precision and 1-2% on your HP34401 - within the ACV limits of the 34401, crest and frequency.
We used it for work on SMPS, invaluable !, from a few kHz/100mA to 20Amps at 500kHz with risetimes that indicated well over 15MHz (fundamental) - all within 1-2%.
Remember to terminate it with 50ohms, remember to degauss, don't through it on the floor, don't use it as a hammer, don't chew on the cable, don't use it as a wrench - do I need to say more?.
Seeing how many questionable (spare)parts available on eBay inspired me to the list above
![WTF? :wtf:](https://www.eevblog.com/forum/Smileys/default/wtf2.gif)
Just handle it like you would your crystal champagne glass, those you only use for special occasions - you don't through your HP3458A on the floor a few times a day either do you - and would you trust it with more than a handfull of digit if you did ?