Hi there just noticed this post, you should find that most internal parts are uniform on these old brass sprinklers, washers are easy to replace if you know where to look, you need to go to a hardware supplier and get an assortment of tap washers they come in many sizes.
Even the famous Pluviette sprinklers that Lloyds made were all made up with British standard pipe fittings.
It is always best to just coat the washers with a little Vaseline, but dont use KY jelly as its not water resistant, keep that for internal door hinges!