They are called brake reservoir grommets and they do need to be replaced once in a while. The reservoir wiggles out (straight up) and the grommets will pop right out and the new ones right in (it takes two). It's an easy job if you don't count having to bleed all the air out afterward. Don't sweat the draining, both chambers will drain in about 3 seconds when you remove the resevoir, be prepared to catch it in a towel or some rags. Clean up the reservoir (I flushed mine with some fresh fluid), wet the two nipples on the bottom of the resevoir with brake fluid so they slide in easier and then align and press down on the resevoir until it seats. Refill, flush with clean fluid and bleed the air out. That's it.


Oh yea, I almost forgot, the grommets are available on Fastlane for about $1.50 each. Look under the brakes tab.

Oooops, further edit.....I reread your post and now realize you were talking about the rubber caps ON TOP of the resevoir. Sorry. I was thinking about the grommets underneath. I believe the black buttons on top are actually switches that trigger the low fluid warning light. you may be able to take those apart and reseal them otherwise I'm guessing it a dealer sourced part. Tell them it's the low brake fluid level switches and I'm sure they'll know what you mean.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold