A rebuild of flippers only requires a few parts - replace the End Of Stroke switches, replace the flipper sleeves, check the flipper coil plunger for signs of mushrooming on the end, a slight bevel should be there - fix with file or replace if badly mushroomed. If mushroomed, then check the coil stop for signs of damage. Then check the cabinet switches' contact faces - replace if pitted. Next check the connectors for the wiring to and from the flippers, related plug connectors, and switches. Make sure the flipper bushing is not cracked, check the flipper shell is not cracked and is solidly secured to the flipper shoe & shaft assembly.
In 99% of the cases these simple checks/repairs will restore your flippers to good solid power.
Do NOT replace the coil(s) unless it is the wrong part number or actually defective, you are wasting time and money and introducing the risk of a mistake which can cause you more time lost in trying to find the problem. The only time you replace a coil is when it has signs of being run hot - and an easy test for that is if the sleeve slides out easily or not. If it slides out easily then the coil is likely just fine. If it is stiff or jammed, then it is time to replace the coil. If the coil has physical cracks at the solder lugs, or other signs of abuse including darkened/burnt wrapper then replace it.
We've serviced a few thousand pinball machines (actually the work order number is in the 5,000s now, but some of those were board repairs) through my shop since the 70s.