Series 3 oil pump fitting

I'm on my third oil pump so want to fit it correctly, just incase this problem is just me being an idiot.

My questions are:

1. is the pump drive shaft long enough? If I push it into place inside the engine it goes in 19.8cm. if I put it in the pump it sticks out from the mounting surface by 17.5cm. Why do much vertical play and is this enough contact for the teeth?

2. There is a missing tooth on each end of the drive shaft. Is this supposed to dictate its position in the driving gears? Can it only be fitted on one position?

3. Do I use a gasket or sealant to fix it into place on the mounting surfaces?

if everything is correct then you cant get it wrong
missing tooth is irrelevant pump isnt timed
theres a gasket err3606

I would check If the missing spline Needs to match up at top and bottom end
It does on the 200tdi I think to allow better oil flow
What part number oil pump did you get, I don’t know about the lengths, I would check if you have any non standard parts such as that shaft, does it match the length below
I think a gasket is normal , also screwlock the bolts in