Sprinkler man says possible crack in drop pipe in pump head. Does this sound logical?
The sprinkler had not been turned on for a year. It works fine for a couple of minutes and then the spray becomes less and then it becomes strong again. This flucuation just continues.

What's the readings on tank pressure gauge while this is happening. Sounds like you turn sprinkler on, water in tank is used and pressure drops until pump comes on. Pump comes on and provide water to sprinlers and builds pressure in tank until pump turns off. Cycle starts over again. The pump cut-in pressure is probably less than the pressure required to make the sprinklers work.

It actually could be either what the repairman said or what Harold suggested. Look at the pressure first. Also, you should check the air pressure in the bladder tank and make sure it is correct with the pump pressure switch setting.

Ideally, you should have enough sprinklers on a zone to keep your pump running constantly while you're irrigating. But, you don't want so many that it doesn't provide enough water to your heads.

The repairman may have been right too. If there are leaks in the suction pipe, it could have a hard time pulling up water. Then, it is able to pull up enough to prime the pump fully, then dies out again if it gets too much air.
Al