My bathroom sink faucet started leaking a few days ago so, I set about to fix it.
First I turned off the cold water, the tap was still leaking, so, then I turned the cold back on and turned off the hot water. The leak stopped. With that simple test I had found that the leak was coming from the hot water tap.
I then turned off both water sources, plugged the drain (don't want to lose any small parts down the drain) and started in on pulling apart the hot water tap which is actually really easy.
One set screw is all that holds the handle on, with the set screw removed the handle comes off and you have the cartridge that needs to be replaced. Fixing the faucet is as simple as pulling the cartridge out and heading to the hardare store to find an exact match replacement before reassembling the tap.
My particular Belanger tap which has been in my washroom for approximately 6 years fell under warranty and the cartridge was replaced for free without any proof of purchase simply because it is a Belanger product.
I have pictures of the procedure as well as the cartridge itself which I will update in a day or so.