Those 30# 'Cylinders' are more then likely NOT leaking....rare without damage to leak.
After filling they can smell of propane due to propane spraying on them from 'bleeder valve' being open and/or when hose/nozzle assembly is disconnected
Propane Cylinders 10 yrs old (older) do NOT need to be replaced unless DAMAGED
Your 30# propane cylinders just need to be re-certified
Visual inspect is good for another 5 yrs. Then another 5 and another 5 etc.
Take them to a Propane Vendor (Bulk---Amerigas, Ferrel Gas etc) and have them re-certified for $10----$40 (pricing depends on Vendor)
Heck of a lot cheaper then replacement of TWO 30# propane cylinders which not only would be cost of replacements but then they would have to be 'PURGED' and then filled.
Just get them re-certified
And check that the 'bleeder valve' on neck of Service valve is closed
(Just SNUG do NOT crank/go gorilla on it. It is a needle valve and doesn't take a lot to shut off)
'Bleeder valve' is indication of liquid level when filling.....fixed tube at 80% level
