Lalizas tri-Color & all-round light

[azuredragon]

I purchased a Lalizas Classic LED 20 All-around & tri-colour light to replace a very old one that was disintegrating. My old one was a Lalizas and externally looks just like the new one. I expected changing the fitting would be straight forward. But I cannot unscrew the new casing from the base. It is just too tight.

I’ve tried letting the base heat up by direct sunlight hoping it might expand a bit. I’ve also tried heating the base carefully in hot water, neither has be3n effective. I haven’t tried to apply any lubricant because I’m not sure what that might do to the plastic.

Also, I’ve only tried to unscrew it by hands. No tools.

Any suggestions?