I just tested my Metolal stored in a 1/3 full sealed glass bottle for 28 months.
It seems not to work anymore,blank film.I tried adding more sodium hydroxide but this did not revive it, failure was not due to atmospheric CO2 reacting with hydroxide in the original mix.
I wonder if the sulfite content of the concentrate could be increased.
(1) Crawley (BJP Jan 6 1961) found sodium sulfite at 5g/L in the working solution is best with Metol as developing agent,it removes the oxidation products.
(2) More sulfite might be a better preservative if oxidation was the cause of the failure.
To get 5g/L at 1:50 dilution means 250g/L sulfite in the concentrate.
This is close to the solubility I looked up 270g/L.
I wonder if there is any opinion on increasing the sodium sulfite in the concentrate.