In my experience, you can splice in fuel hose where there are fuel line leaks in some, if not most scenarios. BUT if it is in a dangerous area, like near exhaust engine etc, you should probably replace metal with metal. It is always better to be safe than sorry.
You would have download the entire internet.
Yes.
Parts could be replaced on a machine without replacing the entire machine.
No, not without replacing the entire sprinkler (and then the hole and feeding line would have to be deeper).
It is possible to replace the air conditioner clutch without replacing the entire compressor if you can find somewhere that sells just the clutch assembly and can get the appropriate tool to remove the pulley to get to the clutch. Try buying a repair manual and looking in there.
Yes. You should also replace the race at the same time.
If it is leaking or rotted
Its hard to really call it "leaking" You will generally start to notice a slow seepage around the valve cover, more commonly in the corners if not circling the entire valve cover. Replacing the valve cover gasket is cheap and fast, and can generally be done for under $75 including labor. ( prices can be higher or lower, generally not over $100 unless Lexus or Cadillac. )
You can cut the ends off of the wires and replace them with aftermarket ends. Check at your local parts store.
You can change the front wheel bearings on your 2000 Buick Regal without replacing the entire hub assembly. You can change each individual wheel bearing, if you choose.
no. the entire thing needs to be replaced
No, a processor is not fixed to the motherboard. Most modern processors are designed to be easily removable and replaceable using a socket on the motherboard. This allows for easy upgrades or replacements without replacing the entire motherboard.