There's been a bit of talk about the Leak tuners in another thread on the Quad FM units.
Here's a site I found some time ago with some useful information, including a TLII schematic for those interested in the inside.
I have to get me one of these, it's about time I zapped my fingers with some valves
Here's a HiFi World article on the Tim deParavicini Stereo decoder
Here's where the Guru's hang out
Another stereo decoder