Just bear in mind that all warranties only exist and are enforceable only in court. For me personally, I wouldn't care where the engine came from as long as it's fully checked prior to install.
For a flood, I personally would like to see
- the walls of each cylinder for any sediment/potential rust build up(seen idiots pressure wash engines, water got in and rusted the bores).
- Condition of the head, valve cover off.
- Condition of the lower engine. Upper pan off.
If all they are doing is taking out your old engine, and slapping this one on the subframe, and bolting it up. 8k is a bit much. esp considering they are probably expecting to keep your old engine+turbo+manifold,etc.
Also, there are slight differences between the M5 and the X5 versions of the S63 packages. Not sure if the blocks are different, but some of accessories are and the oil pump is. (just to keep in the back of head, if you keep the car).
I would say, if time is no a factor. Do reach out to RK(or others), even if that $$ was just for the rebuild labor. They can prob source a LB much cheaper there than here.
Interestingly enough, there is a salvage F86 w/ 63k at pickles. Look like an electrical salvage as 1/4 of the interior is in the trunk. The engine bay is dusty af, could be a good engine. And its in Melb.