Mic the shift fork and the groove it runs in, in the gear, I don't know what the spec should be but if you check both of them (1st/2nd & 3rd/4th) you can see if one is really worn out. Also look for wear in the side of the fork that pushes it into 1st gear. A worn or bent shift fork will cause your issues.
Where the fork is attached to the shift drum (IIRC) there is a bolt and a bushing that rides in the groove in the drum, check there for wear also.
Then the most obvious would be to look at the dogs on 1st gear to see if the are chipped or rounded off, that can cause them to pop out of gear too.
This all based on my experience with my CL72 (250 Scrambler) from many-many moons ago. I hope it points you in the right direction. BTW that CA95 is a 305 motor, right?