Looks like its going well
. How does the tool work? Looks a bit like a bearing puller, bolted to the cam carrier - but I'm guessing you must be able to use it to press new seals in too? 
There's a good video by AGA who make the tool -
https://www.youtube.com/watch?v=YacOx2ydMbI - but basically you bolt the two uprights to cam bearing caps and put the rod between them with the gubbins on, then you use it a bit like a bearing puller in this order:
1) Wind the spring (and valve) down so you can release the rocker from on top of the valve/under the cam
2) Wind the spring (and valve) back up to seat
3) Pressurise cylinder
4) Wind the spring down (leaving the valve up) and rescue the keepers
5) Wind the spring up, remove the tool, and rescue the spring & retainer
6) Remove old seal, install new seal
7) Install the spring & retainer, wind them down with the tool to expose the keeper grooves

Install the keepers - there's a special tool for this but the valves on the Mini are too small, so it's back to the old fashioned grease-on-a-screwdriver method to deposit them
9) Wind the spring back up to capture the keepers
10) Release the pressure, wind the spring & valve back down, reinstate the rocker
11) Wind spring & valve back up and move tool to the next valve
Sounds longwinded but it is only five minutes per valve really and quicker than pulling the head off the car. We'll see if that cures the blue smoke after long periods of vacuum! There's crusty oil on the valve guide tops, which implies it has been getting past the stem seals for some time..
A picture is worth a thousand words and all that - here's the business end of the tool:

And a crusty valve guide top:

The tool comes with several 'feet' that snap on - you use all three on the BMW but only one on the Mini (the shortest); likewise it comes with two sets of 'uprights', but you only use one set on the Mini.