mechanic said my mainshaft bearing is knackered so i bought a gearbox based on his opinion, but can it be sorted without a new box, the cost to get it fitted is pretty big, also if the mainshaft bearing is suspect is that why i have a rough sounding engine, i mean when the clutch is in its so quiet, but as soon as i let the clutch out it sounds really loud whirring noise, can i do anything about this, i know its not the clutch release bearing as i had a new clutch fitted last month, basicly is the new box the easiest option, just scared incase the box i got has other problems that only surface once fitted,