Why does the Haywood pool light always leak after four years at the rear end of the electrical connection?

Are you referring to the conduit? If so, it is probably made of steel tubing and probably not installed to code. In California this conduit is supposed to be red brass. You should have a licensed pool tech or pool builder look at the job to see what it entails for repairs. The red brass if used should be of one piece from the back of the light niche to the j-box which should be located up to 10' from the pool edge and at least 24" above the deck. These measurements may not be exact since I do not know the codes in your area.