1Z gearbox

Hi chaps. I've had my 80 Avant nearly a year now and she's covered about 180K. I say about, because 2 months ago the speedo stopped working and I had trouble getting her into and out of 5th gear. When I pulled the speed sensor out it was covered in metal shavings! I bought some new oil (£50) but when I dropped the old stuff out it was full of gold metal lumps and filings. I wondered if the gearbox from an A4 90hp tdi is a direct swap - anyone know? Incidentally the speedo packing up fixed my juddering problem at mid-revs LOL. I love the car but it doesn;t love me :o(