I've got a similar problem.

Last year there was water in my light housing. Pool Guy looked at and said I needed a replacement.

Ok, since cost was $150. He proceeds to remove bezel, housing, bulb, etc. Then cuts off wire.

Comes back next week and tries to fish wire from new light into light opening. Will not go, probably because there is some type of junction box.

Now I've had my electrician run a completely new wire and next season when the liner is replaced we may able to fish the new light to a new junction box. Here's hoping.