Okay, basics: the group is pilfering a helicopter for what amounts to a suicide run. We've found an ancient cargo-hauler that has minimal security to 'liberate', and a fairly solid plan on how to make it leave its current employer before it sacrifices itself for the greater good.

Only one detail remains: What kind of quirks and eccentricities should a long-serving helicopter have, assuming fairly regular routine maintenance? Something to add a bit of character and maybe throw in an extra challenge for the PCs.

Hidden AI.

Depending on the age, I'd give it either Obsolecense or Obsolete. When my group decided to do something similar (by similar I mean they got an old, used helo) I gave the helo the equivalent of Gremlins 3 for anyone who piloted it. The mechanic spent a decent amount of time and money redoing the wiring and was able to drop that down to Gremlins 1, IIRC.

Scavenged Parts--the vehicle is a Frankenstein of parts used in various operating theaters, and now requires extra love to maintain and repair. Increase all Build/Repair Thresholds by 1 and Intervals by 10%. Each time this adjustment is ignored, apply a cumulative -1 penalty to Handling Tests up to -4.

Mechanics looking inside dont know whether to laugh maniacally or weep.

Hahahahahaha!

I like this one ... I've had characters I'd actually seek it out, with/for ...! IT truly has CHARACTER, not just "oh look, it sucks, ha ha".

You could also adapt the high maintainance implant quality from augmentation.

Sounds exactly like the kind of puzzle my Juryrigger would like.
Will have to ask my GM for something... we need a zeppelin, though. That may require more footwork.

My dad worked on my brother's car for years, and never seemed to need new parts. We found out later that he had been taking parts from other cars and "adjusting" them to work. Which led to such fun things like the heater only working when the radio was turned on, or the kill-switch he installed permanently disabling the rear-defroster.

If you don't need a large one, I'd think the increasing presence of AR advertising has kicked the ad-blimp market in the teeth. Odds are you will be able to findone without too much trouble.