Been having a bit of an inner debate (and outer debate, with my dad) over whether or not to take my 300D on somewhat significant road trips, and just wondering how others approach the decision of whether or not your old diesel is fit for a 500-mile drive (which I'd like to do at the end of the month). I can take my Jeep, and always do, because my MB is not perfect and I'm so afraid of everything and anything that could go wrong. At the same time for all the work I've put into it, I'd love to give it a chance to shine on the road. I always feel a bit of envy when I read about others' journeys and wish I would have the confidence to do the same. I haven't driven my car more than 80 miles at once in probably about five years, even though I take it regionally on the highway a lot.
Sorry if this is a bit more of a philosophical question than a mechanical one; obviously no one can assess the state of my car over the Internet. But what makes you decide if your car is worthy of a long drive? If the vital signs are good do you just pack a few fluids and tools and hope for the best? Or am I an idiot to drive my slightly leaky 277,000-mile baby nine hours up to Canada? My dad thinks the latter, but I'm starting to think rather that I ought to enjoy this car as much as I can while I can, because it isn't going to last forever either way (though I'll do my best).

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)