My old coolant resevoir had the battery hold down moulding broken off some time ago so I went out and replaced the resevoir... This was really the fist time i've ever really been in this part of my car and had to re&re it.
The install was very very easy, but I thought I should let people know that at the bottom of the old resevoir it was VERY dirty. There was a layer of soot right at the bottom. After pouring out the majority of the coolant, i rinsed the inside with a bit of water and shook it around. What came out was chunky, muddy brown and dirty water! I found this surprising as i would think that that part of the car was fairly well sealed and would never get that dirty.

So I guess it can't hurt to clean out those coolant resevoir's every now and then. Just take the battery out, remove 1 bolt and 1 hose and wash it out with a hose

 

Yea the reservoir gets pretty nasty. I'm gonna end up replacing mine too, looks like the battery blew up at some point before I bought it, that acid got everywhere.