Attached is an odd quote for your 4.135.
I looked up the valve cover gasket for all possible 4.135 Perkins engines and found they were all the same so I don't need the serial number.
However, Perkins tells me that this gasket 145610235 is no longer available and they had no suggestions.
However, I vaguely remembered something about Mazda cars using this engine in their diesel offerings in the early eighties so just for fun I went looking for Mazda parts.
So they did use this engine and I can get the gasket through a Mazda dealer in Pennsylvania who specializes in older Mazda parts. Mazda used to purchase the gasket through Perkins (they use the same number) and this guy has eight
of them left.
As I was curious, I went ahead and ordered this part and it should arrive in a few days. I will take a peek at it and if it looks correct, I will send you a picture and you can decide if you want to go ahead with it.