Do the obvious tests first as I've never heard of a leaking turbo seal to cause all those other problems but I do learn something new everyday!!best to replace the lump in one I think,I've got a passat tdi on an r reg you can have for £350,the motor is a cracker on it and it's been chipped to 130 horses and flies,car is well rough but mechanically sound,not 100% sure if it's exactly the same motor but it would need a lot of swapping over as the passat engine sits longitudinally and the golf transverse but I'd be 100% certain it would be feasible,nice motor by the way,looks the part!!