You have a point about service difficulties with this engine, but it does have excellent long term reliability and rebuilds very well.

I have heard the complaint about the transmission before, but I have never personally found this to be valid. Maybe that's because I've driven so much and almost every single mile in a manual transmission vehicle of some sort, so I just naturally deal with whatever shifter traits are present and simply enjoy the fact that I'm not having to drive something with an automatic transmission.

I've never known of any head gasket maladies with the M103. I did the head on mine some time ago, but it was due to corrosion due to the previous owner not changing anti freeze. Most any aluminum head engine is prone to head gasket problem if it overheats. Changing the head on the car was no problem though. Very straight forward, unlike the water pump as you point out.