Typically, this is caused by magnetized coil stops/plungers.
If it "sticks", but you can make it unstick with light upward pressure...there is a good chance that something is magnetized.
Disassemble.
Hold the coil bracket in one hand.
Strike it crisply with a glancing blow with something metallic like a steel rod.
This "knocks" the magnetism out of it. Sounds weird, I know...but it works.
You can do the same for the plunger, but be careful to not dent the part of it that pulls into the coil sleeve.
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Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info