Bruno is great, he's done wonders to my car over the years.. that said, your car sounds sick.. Its a pity you dont have MES or AlfaDiag - at least you'd be able to get some advise on here if you were able to get the codes. Another advantage is that you'd be able to look at the real time data coming from the car %& gearbox which would make it easy to diagnose. Or at least.. easier...
These days, I do most of the work on the car myself, and find the selespeed a fairly easy piece of kit once you get to know it.. anything big, heavy or tedious i leave to Bruno
Parts are 70% cheaper if you buy them from the UK.. even if you get a mechanic to fit, you're still saving.
Regardless of how good a mechanic is, if the car is knackered, it takes a while to get it right. It seems to me the last owner of the car had no idea what they were doing (based on your original post) and as with any car like an alfa, its not a corolla.. its a car you need to understand... and the longer you own it, the more you'll get to know it.
They're not a Toyota, or a Hyundai.. those cars will just work, but they'll also slowly kill you by sucking your soul from you until you're shrivelled up in some shopping centre carpark with 'my family' stickers on the back window (as if any one really cares). That's fine if that's what you want.. dullness. If you want something more, it comes at a cost as with anything.. It doesn't matter what it is.. Lotus, Ferarri, BMW and others, they all need a higher level of commitment, knowledge and understanding, but what you get back.. you'd never get from anything else.
Look after them - as you should with any car.. they'll go and go and go without any major worries.
There's nothing like it...
I don't blame you for being ****ed off, it gets frustrating, especially when you don't know what the problem is.
Let us know what the outcome is..