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DO NOT APPLY POWER DIRECTLY TO THE MOTOR!

Typically the motors have external starting capactors and they need to be part of the circuit.

Get the manual for details of the error codes. And based on the age you can probably get one from Sears.

Sears GDO are made by Chamberlain and have the same basic design and characteristics although the appearance will be a little different (for example the light on different end).

You did not indicate if this is a chain, belt, or screw drive.

Here are links to the current Chamberlain models and you can get the instruction manuals from this page.

https://www.chamberlain-diy.com/diy04/products/buy_online_gdo/0,3818,uid-d2h8b2FnZGxoaA==_1749,00.html

Good possibility that the control board works the same.

Here is a source of replacement parts and it has a link for a cross references between Sears models and Chamberlian.

http://www.aaaremotes.com/liftmaster.html

I suspect the RPM sensor, but it might be binding of the chain/screw/belt and trolley or the motor cap.

Here is what the manuals for the CURRENT models say about the 5 flash code.

"Sympton" motor has over heated; the motor unit does not operate; rpm sesnor = short travel 6-8".

* Unplug unti to reset. Try to operate motor unit, check diagnostic doe.

* If it still flashing 5 times and motor unit moves 6-8", replace RPM sensor.

* If motor does not operate, motro unit is overheated. Wait 30 minutes and retry. If motor unit still will not operate replace logic board."

Chamberlain also has some FAQ and other information under Support.

And the aaaremote place says that it will help, I know with selecting remotes, don't know about diagnostics.

Craftsman GDO code 5 fixed