The time has come. This specific gearbox has possibly been around before you started working at your facility. It's always having issues like mechanical failures and needs more maintenance than your team has time to complete.
The CAD drawings might be missing, the manufacturer might no longer in business to replace the gearbox or components or you might just be switch brands altogether. If this sounds like your situation, you'll need to use this gearbox replacement checklist before replacing your gearbox.
You need reliability--and those "other" gearboxes and reducers can't handle your heavy-duty application. Kick that obsolete to the curb today