I'm afraid that this may sound a bit of a lame question, but how do I disconnect the five round green connectors on the sender unit on top of the main tank? I need to take out the unit to replace th O ring seal (nice smelly petrol leak!) but before I start pulling at them with pliers or prise them with a screw driver and make a mess I would be grateful for some advice on how to do the job propperly. Are they clip-on connectors?