The reason the motor housing broke is probably due to the issue in your video. The slide assembly should move freely with the motor removed as in your photos. I suggest giving Power Gear a call and explain the situation to them. Power Gear 866-574-1688, 574-258-7865 fax 574-256-1248
I do believe the motor assembly, 130-1305, is now obsolete but replacements are available through etrailer.com and other vendors. These parts are under the Lippert name as Lippert owns Power Gear.
To find more information go to this Power Gear website:
https://support.lci1.com/power-gear
They have all of their product manuals available for download and reference plus you may be able to chat with one of their technicians about the issue.
Hope this helps. I think it's a bit unusual the slide itself is frozen up but I'm sure the techs at Power Gear can help you out.