Jonny,
I thought for sure you were with Tom, Joe and me at Starfest when we discussed this--apparently not!
Yes as you've found out the new washer fluid container does not have the brass grommets, but the old ones do. Tom had related a story where he had either that or the brake reservoir (both the same kind of LDPE plastic)soaking in Clorox trying to brighten it up with no success.
I had suggested that he try putting the thing in a home dishwasher with a new product from Cascade made to brighten plastic. Seems that a lot of plastic kitchen items get discolored over use, a lot of having to do with tomato sauce of all things. This Cascade "Plastic Booster" is relative new.
http://www.homemadesimple.com/cascade/products/booster.shtmlI have not tried it but hey, it's worth a shot, right? I've cleaned an astounding number of car parts in my dishwasher during the restoration. I have no idea if Cascade will clean up a brake reservoir or a fluid bottle, but its worth a shot.
BTW by replacing your washer fluid bottle you might run the risk of the "CATCH-22" that I did with my vacuum booster line. A new one does not look like the old one exactly, so you get dinged points for having something not original even though it is 100% Mercedes. The old one you have is too dingy to pass without getting points lost. So, what do you do? It's an educated guess.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored