I had a little VW golf diesel for a long time.... Boy did I ever beat that thing into the ground! but it was a great, very reliable little car. Only reason it ever broke down is that I was always trying to use it like a major pickup truck. Hauling one and two motorcycles on a flatbed all over the country behind 52 horsepower and a transmission that weighed literally less than a hundred seventy pounds. I know cause I've had to remove it before ;)

Anyways, I've run it on veggie oil, without any modifications. I didn't do it often, but it did work and nothing bad happened. I hear there are parts of the fuel train that are sensetive to veggie oils and can deteriorate, mainly a diaphragm inside the mechanical fuel pump up by the engine, sometimes fuel lines depending on what they're made of. Mine were mostly steel, with some small flex-sections out of hydraulic-fluid-rated rubber tubing, so no problem.

Both of those items (diaphragm and fuel lines) are pretty straightforward to replace, pumps aren't that tricky to work on and I'm not anything close to a diesel mechanic. Just remember to mark your timing belt and all your timing sprockets, and mark a corresponding line on a stationary part nearby. I used some sparkly-sorta nail polish my wife donated to the project, because it was durable and easy to see. When you put everything back together, make sure all the marks line up. Anyways that's how I did a lot of diesel engine work. Never had anything go wrong from the work I did.

I dont know if you and/or your partner is at all mechanically inclined, but I strongly encourage anyone to get a little grease on their hands. it's not as hard as it looks. I went from not knowing how to do an oil change (no I'm serious) at age eighteen, to being confident and competent at tearing down and fixing any engine, car, boat, motorcycle, airplane you name it, by age twenty three. And that's just with some instruction books for the cars I was working on, and buying tools along the way as I discovered (usually the hard way) what I needed. No mentors, no classes, no certification, but I'll never need a mechanic's help ever again, unless I'm feeling lazy.

Every survivalist would do well to learn mechanical skills... Although I know we don't all have time or inclination to do it, just like not all of us are master herbalists either. Still, if you can spare the time, this is a great opportunity to add some eternally useful skills to your reportoire, and save a whole lot of money too. Anyways that's my two-bits.
Unless you can find someone to cut you a good deal, any diesel mechanic work is going to make you lightheaded come tab-settling time. Unless you have deep pockets, which I definitely didn't at the time when I owned my golf.

Most likely true. He does run in the winter in the Sierra Nevada mountains though.