[lads_john]

Has anyone done this with the engine still in the car? (i.e the crank in-situ).
I've seen some references to a removal/installation tool with a
chinese finger trap that grabs the upper half of the seal and allows
you to remove/install it.

I'm loath to pull the engine out to fix an annoying leak. I'm beginning
to wonder if it's even worth trying.
Any advice appreciated!

 

[Putt]

Yes, it can be done. The tool is called a "Sneaky Pete" by Lisle Specialty Tools. It is a bit messy, but done carefully it works.