We have the needed replacement slide-out motor for you, Lippert Electric Slide-Out Motor Assembly # LC386322 will replace your P/N 521748.
Please note the linked product review video below. view full answer...
I was able to determine your 2006 Fleetwood Wilderness 315BHS has the Lippert 1621 pin box. For your Sidewinder replacement you will use the Sidewinder 5th Wheel King Pin with Rotating Turret # RP34FR or the air ride option # RP61422. Either of these pin box options will work well on your trailer and provide a 22 inch offset from the king pin to the turret rotation. This provides turning clearances especially needed with short bed tow vehicles. view full answer...