WRT your first question, as Yeoldpinplayer said, the transformers in EM games rarely fail; they are built like brick 'houses. It should be considered one of the least likely suspects.

You reported you have removed the playfield glass before, but not the playfield? First, remove the ball, and then lift up the bottom end of the playfield (just like you might raise the hood on an hood) and place the prop rod on the R side in one of the holes to prop up the playfield. You should then be able to access the components in the bottom board. The transformer on a Gottlieb is most likely located at the left rear.

You stated that you had checked the outlet, but it isn't clear whether you checked it by perhaps plugging in a lamp or by measuring with a multimeter. Do you own a multimeter? If so, you can verify that 115-120V is reaching the transformer input terminals and that the output terminals are reading about 25V and 6V. When poking around back by the transformer, PLEASE BE VERY CAREFUL where you touch with your fingers as 120V can be a nasty jolt. With the multimeter set for resistance or continuity check, you can also recheck the fuses and fuse holders, especially the fuse in line with the power cord hot wire.

Let us know how you're making out.