Col,
Are you doing everything covered in leather? I am going through thie entire interior on my W111. There is a local leather guy who is doing mine and I hang around him quite a bit picking up this and that. Plus he is very good about explaining what he is doing and enjoys having someone around who is interested.
I am saying this because I agree with what Frank says. Installing the leather in your W111 interior correctly is very difficult. Definitely harder than 95% of the cars and made worse from the fact that the interior is hand assembled. That means the gaps are extremely tight and no room for error. There are so many pitfalls I have run across it is hard to remember them all.
Since you are asking for tips, I am assuming you have never worked with leather before? So depending on what you want the outcome to be, dictates whether you do it yourself or have a pro do the hard parts. I removed all of the parts and brought them to him. Normally he won’t do that because he has to adjust the fit to the car. Yes, it is that tight. So I end up taking parts home and fitting them and taking it back for adjustment.
As an example of this, take the leather insert on the back seat ashtray. Seems simple enough. Mercedes allows NO room for anything but skived leather. If you use standard hide thickness, the frame will not go together. And you you have to cut the foam padding back past the squeeze point. I had to take this back to get refitted.
So just one example of the many pitfalls awaiting you. I enjoy doing 90% of the work on the car, but I don’t do this because I KNOW I fall short in experience. Many factors to consider on this.