Grounding the tab (or can body) of a transistor bypasses the internal "solid state switch" that the transistor implements.
Grounding the tab (or can body) is equivalent to grounding the non-banded side of the coil diode.

My money would be on the under playfield can transistor being failed. This is not uncommon.
This section of the PinWiki is for System 80, but applies also to System 1.
You can test the under PF transistor as described.
https://www.pinwiki.com/wiki/index.php/Gottlieb_System_80#Solenoid_Doesn.27t_Turn_On
--
Chris Hibler - CARGPB #31
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