We do almost ever thing in house as far as repairs go. The only time I send some thing out is if were swamped with work and time is a big factor to get a truck or other equipment back up and on the job. Some times I send things out if special tools are required, that wouldn't justify us buying them if they were only going to used once or twice.
As long as you have the proper set-up as far as facilities and tools to do minor and major repairs to equipment, there isn't too much that can't be done.
This is how I aquired some of our equipment, buying things for next nothing, because some other poor soul didn't have the means or the know how on how to fix it