[Ravenser]

It's a very heavy duty solution, but Branchlines of Exeter sell a chassis pack for the Pug giving you an etched nickel silver replacement chassis. This has the added benefit that the loco won't take off like a startled hare

If kit built chassis are rather more than you feel up to - and I'm only just making some first attempts myself - then I appreciate it's not really an answer to your problem

 

[Ravenser]

Jinty2:

The running problems - flat out or stall and seemingly nothing in between - seem to be common to all the cheap Hornby 0-4-0 locos. I've found the little Gaugemaster Combi gives a bit better controlability than a normal Gaugemaster with these mechanisms - not sure why but it does.

On an earlier layout I tried to use a Hornby 06 as a shunter and it was a bit of a painful experience

Recently developed locos from Hornby and Bachmann (eg their 08 diesel shunters and arguably the Bachmann Jinty) have vastly better mechanisms . You might also want to look at the small Knightwing diesel shunter kit (not the bigger Sentinel). Its a very simple plastic kit and with some carving underneath you can get a Black Beetle motor bogie inside with plenty of lead in the bonnet.

Black Beetles are available from Branchlines in various wheelbases for £40 and they really do run very nicely