I found this trail of fluid on the chassis, it looks like it either came from the tranny tail end or the u-joint or the driveshaft. Pattern says it does this while the van is in motion.

my 75 has that same pattern. I put in new u joints and had the rear tranny seal replaced after I got it. I never cleaned it up however, maybe I should to make sure it's not still happening. sorry not to be any real help

I would think its most likely the tranny seal. There isn't much fluid in the u-joint. Just a little grease. Lucky for you the seal isn't expensice and really easy to replace. All you have to do is remove the driveshaft and use a seal puller to remove bad seal and tap in a new one. Just be sure to put some grease or smear some tranny fluid on the slip yoke upon reassembly so you don't trash the new seal by burning it up.

That is certainly from a leaky U-Joint.

There is no way a u-joint would make that kind of a spray pattern. As has been mentioned, there just isn't that much fluid in the u-joint, and it would be VERY difficult for it to leak out unless you had a crack in one of more of the u-joint caps. I second the suggestion that it is a rear seal, and I also think it could be fluid running back along the length of the trans until it get onto the spinning yoke and then is thrown into the bottom of the van. Check for leaks all the way forward.

Well we shall see then

I do see some dirt rust colouring in the residue which would be from a failed u-joint cap seal, water contaminated and finally seal bursted.

Never said I was always right. Once you pull the driveshaft out check the u-joint. Would be a great time to replace anyway. That just looks like a lot of juice. Specially when you think thats just 1/3 or it. The rest is all over the road.

I have similar marks on my undercarriage, but at both ends of my driveshaft, and they existed when I got my Van, 11 years ago next month.

I've never lost any tranny fluid, in my ownership.

That reminds me, I need a new cartridge for my grease Gun.

Yes I agree, many people wouldn't think that there is much grease in a u-joint cap but you most people don't take into consideration that grease expands when heated also with age water gets inside the bearing cap and carnage from there. Worst thing is those greasable joints, that grease just flies all over the place. I'm so happy with my new driveshaft, doesn't leak or anything. But I do have an output shaft seal leak but it doesn't splatter anywheres, my seal leaks a little bit and thing is I have replaced it twice, I never used any RTV when I put the seal in but there isn't a reason to. I don't know what I'm going to do about it, probably just cheap aftermarket seal.