It was of the same type as Mallet's engine, and was made by simply bushing one cylinder of an ordinary two-cylinder simple engine, the bushed cylinder being the high-pressure and the other cylinder the low-pressure cylinder.
More signifcantly, the chassis received a myriad of upgrades, which included variable rate damping and improved bushing, among the many tweaks.
Such bearings can be renewed by driving in a brass or bronze bushing.
A drill pilot bushing comes with the kit to make drilling easier.
Check that the turntable guide and the drive bushing are in good condition.