Toro System Help

My Sister recently purchased a home (Middle TN) with a Toro system - about 8-9 years old. From the notes and documents, appears that this the first attempt to start up the system in 5-6 years. System is comprised of 6 stations w/ various heads depending on location. In that I lived in Denver for several years where irrigation is commonplace, I have been designated the repair person.
A few question to help me diagnose and repair. 1) Many of the low angle rotary heads have become buried by +-3" below the surface from topsoil applcation, age etc. The spray pattern is not good due to the water hitting the turf. What is a good fix for this? Simply digging and clearing the ground around the head results in a pretty ugly conditon muchless a good fix.
2) I can only find one of the control / soleniod valves. Is there a good (easy) way to located them?
3) Many of the heads do not, or partially pop up apparently due to lack of pressue. What is a good operating pressure to look for? I'm guessing that there are either leaks in the system that I have not / cannot find or the overall line delivery pressure has dropped due to the extensive gowth in the area.
3a) Reccomondations in finding leaks? The "watch for puddling and ground saturation" is tedeous and maybe not the best. Suggestions?
4) Pop-ups that do not go back down once the station shuts off - Cause and fix?
Thanks to all. It's been tough to find someone in the area that's interetsed in coming out and fixing it. Apparenty, it is more profiatble to install new system. Mark
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