Definitely not moving freely like LHS so will see if I can take it apart. My searching on the internet has yet to find a manual/schematic, just a handbook with switch matrix and lamp matrix.

I had a look too.  The manual on IPD is fairly limited in what it supplies.

I'm certainly no expert with flippers, but I've just recently put a kit through my Sys 11b (Police Force) and a Data East as well.  If (when power off) the flipper being moved manually is not free / binding then this is definately one problem.

Was the machine previously working fine or is this a new purchase?

I would start by removing the coil stop (two hex-nuts) holding it in and have a look at the coil sleeve.  Also, I would check to make sure the actual flipper bat is not hitting playfield and there should be some movement (up and down) as well.

With the coil out, does the bat / arm move freely?  If so, I would re-assemble making sure the coil is sitting square and flush against both coil stops.