Pos is right, good idea to replace these, however if you forgot to get them fear not, the copper injector washer can be annealed.
A copper or ali washer relies on deforming to make the seal, they are soft metals that crush up and deform to the shape of the mating surfaces.
You can easily get this function back by a very simple process called annealing:
Get some pliers or something. Clean the washer and take it to a heat source (kitchen). Gas cooker? Or some other source of HOT flame. You need to get it hot enough, but obviously not melt it. You need to get copper 'dull red'. Roast it until it glows a dull red.
Swap sides you are holding it because the heat will travel up the pliers, so change half way keeping it in the flame and heat it evenly.
DO NOT quench it in water, that’s it washer annealed.
With ali washers put some washing up liquid on them, when it bubbles and turns to a black deposit that’s how you know you have heated the ali sufficiently.
Clean them up if need be and fit, or take the next steps for a super good seal. This process will only really work on flat washers. Take the annealed washer, and sit it on a clean flat FILE, push the WASHER down the surface of the file once, then turn 90 degrees and push the washer down the file again. You have now crosshatched it. Get some red sealant or the like, and put a little on your fingers, then rub it into the washer. You now have an annealed washer with little channels full of sealant, when torqued down you will crush up the washer and the sealant will just help everything along beautifully.
