Daring DIY enthusiast here...
I always try and attempt to fix things myself to save money, especially when it comes to pc's as it can cost a fortune.
Regarding this. DO NOT WORRY!
It is a relatively straight forward process.
There is not a guide or tutorial anywhere online that i have found however I have just done this repair myself and can confirm it is possible with relative ease and patience.
Follow this guide MacBook Pro 17" Unibody LCD Replacement until the point of pulling of the old rubber gasket, same thing applies for 13 and 15 inch models.
then do the reverse steps but with the new rubber gasket which can be ordered from ebay/china.
YOU DO NOT NEED TO REMOVE THE GLASS.(UNLESS YOU ALREADY HAVE FOR GLASS REPLACEMENT)
Gradually work the new gasket into the gap, pressing it in from either side. The rubber will stretch out and will need shimming back so you can get the corners in.
There should be enough glue left behind from the old gasket to secure it in place, although even if you loose some, don't worry too much as it is more of a press fit than it is glued in. You could always use a glue if i wish, but choose the right one.
Take your time and make sure it is secure all the way round.
Put everything back together and hey presto, a fix or around £10.00!
Here is the link to the gasket i bought for my macbook pro mid 2012 unibody model.