Seems like a problem with every big trip for us. I almost look for it just to get it out of the way.
Going from southern LP Michigan to the UP on Lake Superior 4 years ago, our truck died....completely. We were 3 hours from home and had to pull over on the side of the expressway. Ended up taking 5 days to fix the truck at a local shop, we stayed in a local cabin and completely missed our UP trip. We still had a nice time with plan B, however and finally made it to the UP the following year.
Going from Michigan to Kentucky 2 years ago, our truck (different truck from the attempted UP trip) started overheating when we were 7 hours from home. We managed to nurse it to the campsite. Found out it was a clamp that came off of a hose. Luckily fixed it for under $100.
This spring, at 11pm at night, when we planned to leave for the Smokies at 6am the next morning, I found water all of the bunkhouse. Apparently our outside kitchen hose was broken from the winter. We had to fix it before we left and got a late start, didn't leave until 9am. Got to our campsite at 10pm that night. 5am the next morning, our LP/Carbon monoxide alarm started going off. We didn't have the LP or furnace on at all. The detector was bad. We replaced it that day, but we were up for the day by 5, when we'd had a late start the day before from other issues.
Could be much, much worse, but I think I will be suspicious of any trip that just seems to go too right.