I was wondering how long this part is expected to last. I have a Janitrol GMP100-3 that is a 100,000 btu unit. The Venter Blower Asm. was replaced after about 4 years, due to the bearings making loud howling sounds. It is now about 4 years and the Venter Blower Asm is howling again and will need replaced. Is this something to be expected. Thanks for any information.