A likely problem will be fogging, regarding which Ansell Adams, says "The fog level that comes from age, heat, and so on, can often be reduced by adding Potassium bromide or Benzotriazole to the developer." I quoted that in DIY B&W on Flickr, which as usual was of variable quality so far as advice goes. What this Kitsaplorax had to say in that thread about Glycin is interesting, and I'll look at replacing Metol with it in the future, perhaps, but I can't find any to buy, online, this morning, so I'll go with Potassium bromide for now, (which, yes, is the stuff allegedly put in soldier's tea).
Silverprint sell it, Gawd bless 'em, for a couple of quid, but in view of their £6+ postage charges I did some other shopping whilst I was there, getting some Rodinal for those times when I'm too busy to make up my own developer - it's all the rage in DIY B&W and is made of chemicals which I don't have, anyway. I got a roll of Rollei IR, and various (cheap) b&w films to try out. I looked at Rollei Crossbird and Nightbird 127, but at £9 a roll it's a bit much. The Nightbird is horrible red, like Velvia. You could experiment with b&w chemicals, but not at that price. Looking at 127 because in addition to the Baby Brownie, I've just got a Brownie Reflex.
Abstract of Silverprint invoice below, for reference:
76526 POTASSIUM BROMIDE 100g £2.27
71365 RODINAL 125ml. £4.08
54612 FOMAPAN 100 135-36 single £1.86
54648 FOMAPAN 100 120 £1.84
801 Ektar 100 135-36 £3.23
58270 APX100 135-36 single £2.36
15157 ROLLEI INFRARED 135-36 £5.83
Net Order Value £27.72
Total VAT £5.55
Total Order Value £33.27