In this video I show you how to repair and replace ball bearings in a linear bearing provided the housing is not damaged and the bearings by mishap or accident have popped out. 
Awesome! I got the same bearings from an old Flex Leg Press. Maybe you can make a video how to clean the bearings when they were used 20+ years! That would be great!
Haha!!!! I have a ton of flex equipment. Did it work for you? So I had an old flex leg press I did the same repair on. The guy on the east coast left it out in his back yard for years in rain and snow. It was a rusted mess. I restored the whole thing. And bearings were rusted as well. Use an industrial spray lubricant like liquid wrench or similar. Soak the whole bearing with it and put in a ziplock bag for a day. Then take it out, put mechanic nitrile gloves on (cheap harbor freight) run your finger on the inside of the housing pushing the bearings making them roll. They are stainless steel. They will start rolling if you need more friction put a thin rag on you finger and push the bearings. You can get it like brand new with some patience. Glad I could help.