What is your thought on replacing hand held equipment? Do you let it get a certain number of hours/yrs of use and then replace it regardless of its condition? My Shindaiwa stuff is getting old...but it just keeps running. The occasional cleaning of the muffler, or other little repair...but they still start easily and run reliably. I find it hard to justify buying new stuff when the old stuff is getting it done. Whats your thoughts?