Problem with Transaxle
 

When my 2000 Boxster S 6 speed is cold, it can grind going into 1st, and will go into 4th fine but will pop out when I release the clutch. Not 2nd or 3rd or 5 or 6. 1st is fine after a block of driving. 4th can be a problem for a few miles. It does have 190,000 miles on it. I've had it since almost new.

I have searched online and I have found various people who claim that sometimes the shifter needs to be adjusted - and there are Youtube videos of people getting the little clip on tool that holds the shifter in the center, and they remove and reattach the cables.

I feel like that is meaningless. I installed the shifter many years ago. As I recall, the shifter has no physical stops. So as long as it's reasonably centered, it will float to the spot that the cables want to be at rest. And it doesn't change the ends for full shifts.

Does that sound right? Or am I missing something and it is worth pulling apart the center and doing this?

I also have a 2000 S 6-speed and it is similarly problematic when cold. Mine doesn't grind but it takes a lot of force to get it into any gear for the first few minutes of driving. Once I have diven a bit and forced it into all the gears it is fine. Also no problem on hot days.

The adjustment may help when you are hitting the end on the shifter assembly before you hit the actual gear position.

When in doubt on this, the easiest might be to pop the cables of on the transmission side and feel how far the shifter will go. If this is close to where you feel the gear positions, it might be an option.

But as you have some issues on 1st and 4th, it doesn't sound too logical that it is the shifter.

As you mention it only happens when cold, my first action would be to get some new oil in and see whether it improves. On my former, old BMW I used to swap the oil yearly and it was always worthwhile (now I just keep it in as it is supposed to be lifetime oil haha).