master cylinder view is cracked

[joshf123]

i have accidentally cracked the small white plastic circular piece on the master cylinder and now brake fluid leaks from it. i'm not sure what that part is called. it's a little view where you can see your brake fluid level. i'm trying to find the cheapest way to replace this and stumbled upon

http://www.powersportspartsonline.com/S ... 23207.html

i'm thinking that would replace the outside part of the master cylinder and in effect replace the part i cracked. i'm not going to order this until i know it will fix my problem. the guy at my local bike shop said i would need the entire assembly which is $130. i hope he is mistaken