I must half agree with Lee.
You don't need the latest and greatest, but don't drag out the first
reg your great great great grandfather passed down either.
After 50 years or so it's time for the display case.
Depth has no bearing (sport), if it works in 5 ft it will work deeper.
The other thing to note is if the air bleed is working from the first
stage your good to go.
I don’t need to mention hoses, that’s common sense.
The second stage may be your problem.
Check to see if the diaphragm is rubber (it can fail with out notice,
they dry out)
If it is it needs to be changed (rubber is no longer used (all brands)
in second diaphragm for this reason).
Generally speaking rubber is black.
The newer one is silicon (opaque).
Check the exhaust valve for softness and cracks (any doubts change)
That said Sherwood has be rated the safest reg in many USN tests.
Very few moving parts and seals.
Cheap and easy to service.
I use them for single reg sport diving.
I don’t use them for tech dives because the hose porting and din are
not suitable for those types of dives.
That and the dry bleed drives other tech divers nuts.

T