What do you mean by "the lid"
The pump really has no lid. Do you mean the lid on the skimmer that is attached to the pump or the lid of the filter housing itself?
You could *try* using a soldering iron, or similar device, to melt the crack closed, but chances are it will not work, or will work, but not last too long.
If the crack is in the lid of the skimmer basket, then you should be able to get a new one either on line or at a pool store. If the crack is in the top of your filter housing, you may be able to get a replacement, but chances are it will not be worth the cost compared to the cost of an entirely new filter housing.
-dave