78 Benz Oil pressure

I just got a 78 diesel mbz. (some back ground) 212,000 miles. From gathering information from where I got the car the heads were re-done (and some other minor work). I don't know of any transmission work but my father in law is looking for the service records today. I was wondering if the following was normal for this car. The oil pressure gauge, in idle, is somewhere under 30 but when I accelerate the gauge shoots up to the highest pressure (45) and looks like it could go higher if the pin where not there. Is this normal?

I also have a slow oil leak coming from the oil pan and another small leak coming from a box (maybe transmission) about 2 or 3 feet behind the oil pan. Is this something that can be worked on at home or do you generally have to take mbz in to get repaired? I've heard that when you fix one leak the engine finds another weak point to leak from, is this true and how should I handle the leaks?

Any recommendations on what type of oil to use?

Last question: Is there some links to manuals or websites that can help me better understand maintaining this type vehicle?

Thanks
kb