I am doing my Tech IV right now. My baby daughter is playing with the old tan material, no doubt full of carcinogenic adhesives.
I just got the cheapest material, it looks very well cut. It seems to stick fine even though I haven't removed all the old adhesive. I do need something to remove the gunkier, stickier stuff, rubbing alcohol isn't doing the trick.
Linhof uses some thing metal foil and some filler in the recesses under the covering. I am not going to worry about it, as this is a beater caemra without the rangefinder or viewfinder gizmos - I just covered the holes up with an extra layer of tape, which shows through but doesn't look bad. Nobody will mistake this for a Technika 2000 though.
Naphtha is what I use to remove old adhesives. Use in a well ventilated area away from sparks or flame.
I got a nice e-mail back from Morgan Sparks about getting a natural leather covering. He noted the problems about paring the leather down to an appropriate thickness and the issue with the grain not looking right with most natural materials on the Linhof, because of the number of surfaces to cover. He said that there was an appropriate ready-made leather that can be found on some German pre-WWII cameras, but he hasn't found a modern producer for it. I'm going to ask an acquaintance who is a book conservator if he knows of anything. He estimated $130 for an embossed leather covering and $175-200 for kid leather for the Technika.
I wonder what they would charge to apply a kit to a Linhof? While it's probably very easy to apply, I've not had good luck with glue preapplied, it tends to stick when you don't want it to, and not stick when you want it to! And this way, if it comes out not looking perfect, I have somebody else to blame!
Of course, at the moment the coverings on my Linhof are like brand new (other than one of the itty bitty rectangles below one of the grafloc sliders which fell off), so my interest in recovering it is only for later down the road when more panels fall off.