On a high-end pipe, even a factory one like a Dunhill, the mouthpiece will have been turned and finished together with the briar shank so that the two parts fit together smoothly and seamlessly. You can fit a replacement, but it won't be as nice unless it has been fit and finished by hand on to your pipe. A good pipe restorer will do that, and it will cost $40-50, especially if you want the Dunhill white dot logo on it. If the current bit hasn't collapsed and is is usable, I would keep it even if it has some tooth marks. Clean it (inside and out) with Everclear, high proof vodka or rubbing alcohol (I use the latter, but only because I don't have either of the other two). In fact, you should spend some time running some alcohol dipped pipe cleaners through the pipe to clean it as well and do the same with the inside of the bowl. If the pipe wasn't cleaned before being sold to you, you will be amazed at how much gunk is in there. Note that the bit is probably made of hard, vulcanized rubber and it is normal for it to discolor with an ugly, brownish, greenish haze over time. That is no big deal and can be fixed yourself or by a pipe shop. It won't affect the smoking, so why don't you see if you like smoking the pipe at all. If you do, then you might want to spend more effort on the cosmetic cleanup.
Edited by dopey - 8/1/11 at 7:54am