A couple of comments: -
2. If you don't know the S/N how can you be sure the Parts Manual you have is the correct one for your machine..? Just sayin'. As a comment there are no less than 15 different Parts Manuals for 950G of different Serial Number prefixes.
Not to belabor this point but with all the running changes Cat and others make on a machine the serial numbers is about the most important piece of information when looking for help and information, I as well as Nige try to push this point not just for you but the next guy who needs help.
To go off on a tangent, which I tend to do too often. Just the other day on a walk-behind snow blower form a guy was asking how to change a belt on a ST824 machine(no, not a Cat). Well I looked up that number and found that the manufacture uses the same "sales" model for at least two very different machines! One had one belt to drive auger and the wheels and another that had separate belts for the auger and the drive wheels. Just imagine how upset this guy would be if I or someone else went into details on the project but it was for the wrong version on the machine!
5. If you went to the expense of buying a complete new filter head then I would personally buy a new breaker relief valve for the top of the hydraulic tank and have done with it. On loaders we used to replace those valves on a 2000hr PM. They suffer a lot more than you would imagine.
This also is an excellent idea, especially if like many machines the people taking care of them don't know the part even exists so it has been covered with six inches of dried mud for years!
Also at times even Cat does not have engineers who have a good understanding of the conditions these machines work under. More than once I found it important to relocate a breather to get it to a place one could actually reach and not get buried in dirt and dust in the matter of a couple weeks,