Unfortunately the M16 plus 4 has the water pump as a part of the cam belt drive, later the water pump was changed to auxiliary belt drive on the later T16 engine. The turning of the engine by hand shows it going from tight to loose,,,,have you tried taking all plugs out and turning engine by hand. As rechard says have you lost teeth on the cam belt.
looks like lots to look at please report back with what is found, if youre changing cam belt its worth putting in a new water pump!
Manuela etc required then I may help, my engine is the T16.
