I can try and help on the slide. Many have a built in overload clutch that ratchets, trips like a drill chuck on a battery operated drill motor. So when you reach end of stroke it trips, goes, cluck clunk and you take your finger off the button. Not all do this, mine trips on the way out but not on the way in. I have a Lippert slide system and yours may be a Barker as Sunline changed brands over the years. I also do not know the model of your camper to know if you have a super slide or a mini above floor slide. They built the above floor ones different then the super slide that was level with the floor. It helps if you can tell us the model of the camper and I'm guessing it is a year 2000.
When you hand crank, again, many bypass the overload clutch and you are direct drive right on the Acme screw. The mechanical advantage is extremely high and cranks by hand easy where the 12 volt motor, works. Be careful when hand cracking when you hit something you can tear up the slide drive and never realize it as it cracks so easy. The worst is going the wrong direction against a fully open or closed slide.
If you can take and post some pictures of the slide mechanism I may be able to help more so I know what you are up against.
The slide seal, again pictures help to what style you have.
Here are "some" sites to start the hunt. RV dealers can help too but you need to take a sample or pictures with dimensions. There are lots of different kinds of seals. Every brand uses something a little different in some cases and even Sunline may have changed types over the years. These links are close for a year 2003 to 2007 Sunline Super slide. They may fit older ones but I do not know for sure the profile used on 2002 and backwards.
Flap Seal Product Builder - Flap Seal - Trim-Lok
Slide Out Seal for Pop Up Campers 19-G8135
One thing that will be the same from any of them is cost. Do not be shocked at $6 to $12 a foot. I will need a new seal in the near future and soon will be starting the hunt for the highest quality, right size and best price.
The roof, I cannot help you on that one on where to buy a roof done. In my case I would do the repair so it is only materials costs which is not that bad but labor is expensive. Some others may be along on the roof costs as they have had them repaired. Generally the small independent repair guy is better then the big RV dealers.
Good luck and hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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