The 503 was in trouble from the start.
While it was "preserved" at withdrawal, the Local Authority sponsoring it soon wearied and had it stored in the siding under the Mersey for a decade. When a preservation group took an interest, the owners only released two cars, retaining the driving trailer for conversion to a cafe and childrens play area. Much dismantling was done and items stored in a container that was subsequently dumped when the cafe idea flopped. The remains of the carriage were then sent to the award winning Coventry ERM, with little good will from Merseyside, whose hands remained firmly in its deep "City of Culture" pockets. The unexpected loss of the Coventry site without compensation (it was said that the "heritage" element wasn't local so clear off..) meant that only the new site at Margate was available. With so little direct support (probably low single figures!) for the unit, the work on the more popular 4SUB was delayed, hence the necessary but regrettable action. Perhaps Mid-Wales may be a better site for a Merseyside unit than East Kent.
Still, better luck to the 502 Friends and the 507 Group.
WAO