These guys don't know what they are talking about. This is OBVIOUSLY a regulator problem. Not knowing the age of the car, I can't say if the regulator is worn out or there is a short or what, but it's your regulator.
Take it to Esso and ask them to test it with a standard can of steam. If the test is positive (I'm 99% sure it will be), you'll have to rebuild your regulator, but don't do it at Esso. You can do it yourself, assuming you have a set of bookend wrenches and a little elbow grease.
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