Thanks Infosecdad for finding these:
2005 LGT Stock side-feed injectors:
9263K776 Chemical-Resistant Viton Fluoroelastomer O-Ring, 3.5 mm Wide, 20 mm ID, packs of 10
9263K124 Chemical-Resistant Viton Fluoroelastomer O-Ring, 2.5 mm Wide, 8 mm ID, packs of 10
Ordered a pack of ten of each from McMaster, should be here Tue.
Then I can be sure, they are good; thought I would leave this here in case someone needed the sizes.
The ones I carefully removed to measure are quite dry and cracked.