All Dizzy's are susceptible to wear..my guess is something was worn inside it. Points dizzys need a little more maintenance however i find them more reliable than the Lekky ones. For example my 3K dizzy has seen more than its share of high rpm without trouble.
With the gearbox, you'd rather take out 6-7 bolts around the bellhousing and mess around with an input shaft than undo the tailshaft, crossmember and gearshifter and have it all out in one hit?