Professional Clippers

I am a dog groomer and have always used Oster Clippers am now finding that the blade head is always coming loose. Have regularly been oiling and greasing them but still the blade head becomes loose. Can anyone recommend another make that is more man for the job, need heavy duty reliable clippers, as going through a new pair every 3 months and not satisfied with the Oster A5 now. I would be interested in other groomers opinions on this subject Thanks