To tell him (a friend) to get stuffed next time?

[TopShagger]

I can't decide if this is more of a "what do you reckon" than an AIBU. Maybe it's a bit of both.

So, long story short, a friend of mine, who I and my family have done a LOT of favours for (and I do mean a LOT) isn't being as forthcoming as I'd like to think he would be now that we need (not want) a favour in return.

We aren't in the game of storing up favours, or doing them just so we can get one in return in case anyone thinks that. We're disappointed rather than pissed off. Basically the response is that he's prioritising his own shit. None of us said that to him about any of the countless times we've helped him when he's wanted something. We've usually dropped whatever we were doing and gone to help, often late evening, frequently weekends.

Am I being a knob or am I at least somewhat justified in being a bit miffed about this?

I agree with @roussette's first paragraph. It isn't necessarily to do with conscience even, though, he may not be conscious at all of how you see it. Or he may be aware but see it completely differently from you, it is possible, and not wanting an argument. But in any event it would mean you'd know where you stood for sure.

Whilst I can see that he seems a selfish dick, I think you have been not very savvy here. If you’d charged him for the work you did, you could have paid to get the car fixed.

This is a very good point, for the future.
Small favours may be fine, but huge favours costing loads of time and £££s should be a no-no.
If anyone asks, tell them you're busy. especially if it's someone who's brought the problem on themself!