Well bleeding down

Have a deep well 300 ft with a Gould 5ES submersible 1/2 horse 3 wire pump. I noticed the pump coming on and off occasionally even with no water use. This has been going on for quite some time and seemsed to be getting worse. Since the pressure tank, gauge and pressure switch were all coroded and leaking I decided to replace them all. I did find the check valve near the pressure tank leaking back and also the pressure tank defective also. My fear was the bad check valve may have been masking a bigger problem and it was. When the pump is not running the water bleeds back down and takes a some time to pump up again. With the defective check valve the pump would run every so often and mask the problem. My question is how can I check if I have a well pump, drop line or other leak back to the pump. Does the pump itself also have a check valve. I dont see any wet spots out in the yard leading to the well.
Appreciate any help before I called the Well people.
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You prove my point that a check valve at the inlet to the pressure tank only masks and thereby prevents timely indication of a problem. If the check at the tank was leaking, then you've proved a leak between there and the check valve in/on every submersible pump I'm aware of.
It may be the pump's check valve or the plumbing back to the pump. The only way to find out is to lift the drop pipe and see if it's full of water or add water and see if the level falls. If it stays full that says no leak (with the little pressure of the weight of the water in the pipe) from the pitless to the pump. It also says the leak is between the pitless and the pressure tank. If the drop pipe doesn't hold water then the leak could be a split in the plumbing, a loose fitting or the check valve is blocked open or damaged. Call a well driller or pump guy (under pumps in some yellow pages); most plumbers are not a good choice for this type problem. Some are and their yellow page ad will say if they do submersible pump work.
It will take some effort to lift the pump and plumbing from 300'. I have winch and a machine but IMO there's no way one guy is going to lift it and then pull it up 5-10' and hold it unitl you decide where the leak is and what you're going to do unless you've done this a few times.
But how do you get a 1/2hp 5 gpm pump to work at roughly 300'? Usually a 1/2 hp is only good to about 150-180'. Do you know how deep the pump is set at? How about what the drop pipe is made of? Galvanized will required a machine or derrick truck. With a leaking check valve and a couple guys and a way to stop and rest.... maybe with PE tubing. With the drop pipe full of water... maybe if they're young and foolish. LOL
Gary Quality Water Associates
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