Well i think its not possible to remove it without destroying it as it is very tight.

Anyway, I did not grease the mech seal to insert it, I just sprayed some silicone spray when assembled the pump shaft and this might have reduced the necessary friction between the pump shaft (where it has the white small seal) and mech seal.

My advice to you is to disassemble it, give a good clean with soapy water on the mech seal and pump shaft to remove any grease on the rubber/shaft, dry it and reassemble it.
Also make sure that the mech seal is fully inserted into the pump case.

Hope this can help you