Re: loss of first and second gear
Most likely linkage. Mine was so sloppy, that it hit something in the tunnel before 2nd gear would engage, so it was not possible to engage it.
Btw. if you do take out the linkage - I highly recommend disassembling the shaft, especially taking out item nr.12 from the shaft and lubricating it, so that item nr.21 rotates freely.
On my 75, it was very hard to rotate item nr. 21 - this made finding gear 3 & 4 quite hard, because the linkage would not self-center in neutral. After disassembling and lubricating everything. the gearchange is improved substantially. although there is still some slop in the linkage.