F type nearside door mirror problem

[Glaf]

My nearside door mirror just seems to magnify the view and is pretty useless, especially when there is already a recognised blind spot problem on the F type. The drivers side is fine so I'm wondering if the glass has been replaced at some time by the previous owner.

I've noticed replacement mirror glasses on eBay, some convex and some with 1/4 of the glass specifically for the blind spot, I'm not sure about the quality though.

Does anyone have a similar problem and have you replaced the glass? If so is this an easy task?