The car is gorgeous. Small details such as clamps can be corrected with pocket change and shouldn't seriously enter into an evaluation equation.
I've photographed car details before, and can tell you that under certain lighting conditions, silver finish appears gold and vice versa; so unless you see the car in person, don't assume. Also, that photograph you can see on the website doesn't provide enough detail to make serious judgment calls. On the screen it is about 8x10 at res 72, which is pretty low. Most camera phones will give you a lot better results.
The original brake reservoir isn't available to my knowledge. The original ones don't often look pretty (how often do we see questions about cleaning and brightening the plastic?) so it's easy to understand why they installed the one they did.
If the work was done by the Mercedes-Benz Classic Center, they can ONLY use, without exception, parts sourced from Mercedes-Benz--even if those parts are far away from original appearance, and a reproduction that looks perfect to the original is available, or can be made.
If one were to take a good driver, or even a great one--to Motoring Investments, Kienzle in Germany, The Classic Center (Germany or USA), Hjeltness or Gernold at SL-Tech and ask for a ground up restoration, you would be in that kind of money. Just ask the Gary Jarvis about his 250SL featured in the current issue of The Star...