A lot of this is due to the grease applied to the runners. It's a dust magnet.
Use a damp cloth to clean out as much as possible and then use a spray cleaner to get the rest.
Get a tube or tub of lithium grease and apply it into the runners with your Dad's toothbrush.
Treat the seals with rubber treatment. This keeps the rubber seals soft and pliable.
Clean further back into the roof guides also. You'll have to pull the rubber seal to one side.
Treat this rubber too...
...as it can easily become damaged and begin to splits as can be seen here.
Operate the roof a few times to spread the grease around and you are done.