The tamiya j motor is to be stayed away from (
http://goldstarstockists.net/live/ca...95e084c5d0aafb)
Not even worth 1p let alone £15!
The lastest silver can (black end bell) motors are to go for!
http://cgi.ebay.co.uk/Tamiya-53689-5...item58845ce4d6
http://cgi.ebay.co.uk/Tamiya-RS-540-...item3ca778b80f
Hope that helps you
The main diffrences are inside the motor's ie winding and how the brushes are made.
The latter two motors are made by mabuchi which is a huge maker of motors over in japan
So its down to you now on which one to buy