not necessarily, but it wont do any harm
also, its good to keep a spare just in case
if it isnt the gauge itself that is leaking, and just where its been insufficiently well screwed in with loctite, then just clean the threads well and re-fit it with good loctiting.
in hindisght i feel your ripping of gair for selling a leaking air system was uncalled for if all it was was a problem with the gauge needing to be screwed in again properly.
reading it made it seems like he had sold an unsafe system / one in need of seals replacing or servicing.
air system i bought, gauge was bust - an extra £10 for the gauge, but they arent the most robust things and royal mail was probably to blame. i didnt even mention it to the seller....
but there you go im not judging just saying before you flame someone who i happen to know...