Weight of the tow is but one factor to consider for safe towing. If your Buick is right at 5k obviously you're at max on one factor. Many on here will say they knew a friend who had a friend who's second cousin on his mother's side towed over max for years with no problems so it should be ok. I usually don't like pushing my luck with things like this. IMHO, you could tow the Buick with little or no problems but you'll be stressing the motor home. Things like the motor, trans, frame etc. How it will respond to that stress is unknown. Personally, I'd look for a lighter towed...I can tow up to 10,000 but my toad weighs in at 3180 wet......Dennis