GT6 Gearbox

In the early part of the summer I was driving home and I found that I
could not shift in 2nd & 3rd.  This gearbox is a MKIII GT6 with OD and 2
years earlier I had the same issue.  It turned out to be a broken
circlip holding the 2nd and 3rd gear cluster together on the mainshaft.


The question is, I am about to pull the box out of the car, is this
common with these gearboxes?  I only have maybe 1500 miles on this last
circlip, has anyone done modifications to beef up this area?

Thanks
David Templeton
'59 Triumph TR3a
'74 Triumph Spitfire