Cannot get the decora 4 way light switch to work - 2 of the 3 switches work but cannot get the 3rd to work. Replacing regular toggle switches which all worked but wiring different for decora switches.

Decora 3-way and 4-way switches do not wire differently than toggle-type switches.
Instructions below are tedious but will accurately guide you to solution.

Let's break down the problem starting with 3-ways.

1) Start with 3-way switches:
Old 3-way switch has 2 brass screws and 1 dark screw
New decora has same color screws.
Wire that went to dark screw on old device must attach to dark screw on decora device.
Other two wires can attach to either brass screw.
Wires that attach to brass screws are travelers ... these wires travel to the 4-way switch.
So there are 2 traveler wires at each 3-way switch.

2) Let's test if 3-way switches are wired correctly by taking 4-way switch out of equation.
We will resolve problem with 4-way switch after 3-ways are correct.

There are 4 wires at the 4-way switch.
These are the 2 traveler wires that arrive from each 3-way switch.

At the 4-way switch, 2 wires arrive in one cable, and 2 wires arrive from another cable.
To say it differently, there are 2 wires from cable1 and 2 wires from cable2.
Connect 1 wire from cable1 to 1 wire from cable2 with a wire nut
Now connect the 2nd wire from cable1 to 2nd wire from cable2 with another wire nut.
So now the traveler wires are connected, and the 4 way switch is out of equation.
Turn on power, and click 3-way switches to see if both switches turn lights on-off in all positions.

Do your 3-way switches work correctly?

3) If 3-ways are not correct, then you have wrong wire connected to dark screw.
First thing to check is if you can identify traveler wire colors by looking at wires at 4-way switch.
Remember, traveler wires at 4-way switch go back to 3-way switch and connect to brass screws on 3-way switch.

4) If you cannot tell traveler wires by looking at 4-way switch, then you can try different combinations until both 3-way switches work.
Or you can test: disconnect wires from one of the 3-way switches. Separate 3 wires for testing. Move other 3-way switch to down position. Turn on power. Test each wire to bare ground wire. Mark wire that lights up. Now move other 3-way to up position. Test each wire to bare ground wire. If same wire lights up each test, then that wire goes to dark screw. If different wire lights up, then mark that wire. The two marked wires are travelers, and they connect to brass screws. Other wire connects to dark screw. Repeat identical test for other 3-way switch.

At this point your 3-way switches will work, if light bubs are not burned out.

5) Last step, the 4 way switch.
Remember from step above, that 2 wires arrive in cable1: These 2 wires connect on one side of 4-way switch. The other 2 wires that arrive in cable2 connect of other side of 4-way switch.

Add a comment if you need more help.