I know what you mean about a stiff shifter boot, it was below zero and when I would start and shift my car the boot ripped in multiple places!

So genuine leather is the way to go. I bought one from Redline Goods, turned out quite nice. I don't have a photo handy, I can take one. But here you can see their installation instructions and how it will look-

Mercedes 240D 76-85 shift boot installation - RedlineGoods leather shift boot store

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1983 300TD - 202k with 5 speed Getrag conversion