Anyone please help me with what water pump I need

The only thing I can suggest is to go to your nearest lunar dealer and take their advice.

Good luck and perhaps other club  members who have this type of water input can help you further.

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                        Because of the year your best bet is a Caravan Breaker there are many around. If possible try and see it before you buy it.

Perhaps change to a modern filter and pump?

There are two parts to your system. There’s the plug in connector, which you can retain, and there’s the submersible pump which you can readily buy. If it’s 12v anyone’s will work. You’ll need to cut the original one’s cable near the plug in connector and join in the replacement. Soldered joins are best, sleeved with heat sensitive shrink sleeve with, ideally a squirt of silicone sealant introduced into the sleeve before shrinking it.