Are "Genuine OEM" replacement parts necessary for a furnace?
We have a Trane XE70 gas furnace, original with the house (~22 years). I hired an HVAC tech to perform seasonal maintenance and inspection. He recommended the capacitor be replaced, because the reading was slightly below the "acceptable" threshold. He also noticed the blower motor was making a "clanking" noise at start-up and shut-down, which he believed was a bearing going bad - and recommended replacement of the blower motor as well. Due to the age of the unit, his final recommendation was replacing the entire furnace.
I found a web site that sells "Genuine OEM" Trane replacement parts specific to my furnace model. However, the prices of these parts are a LOT higher than generic/no-name parts on other sites.
Is it necessary (or recommended) to replace with OEM parts? Due to the age of my furnace, is it worth replacing these parts at all, if we plan to purchase a new furnace next year?