Alfa Romeo DIY gearbox rebuild?

[peaktorque]

The car is a 2007 GT Q2 1.9 JTDm.........

It's is jumping out of third and forth gears.

I'm an engineer by trade, so I'm fairly well equipped in the tool department

I've rebuilt engines, but never a gearbox, so I was wondering if it is do-able without any 'special' Alfa tools (I've been told that they are necessary)

I don't really want to go down the second hand route, or pay someone to do it when I could do it myself (I'm a bit tight )

......or shall I just bite the bullet and get it rebuilt with a nice 12 month warranty?

Thanks.