Some UK outline for a change:
I picked up an old Hornby HST from Ebay a while back, it's in good condition overall but the ringfield motor was little knackered! A good service didn't improve matters much and getting a replacement was proving difficult as well as potentially expensive, then I came across this low cost alternative which uses a motor from an old CD drive. Here's the link...
http://web.onetel.net.uk/~johndent/ringfield.html
I installed the motor as described except that I had removed the old magnet which left a lot more space around the motor, which I simply filled with blobs of hot glue. Here's a pic:
I wired in a bog standard Hornby decoder and was amazed at how well it runs. Here's short video of it in action, sorry about the low quality as I took it on my phone....
I considerably increased the weight in the loco and as you can see it pulls a 5 car rake as well as a driving trailer with no problem at all.