Regarding the Sims/leasing company embargo on sales, I have not yet been able to confirm with my contact that it was indeed Eversholt, but another source has suggested a possible reason - traceablility.
Although this wasn't elaborated, I guess that there was a possibility that spares, if removed and sold at a breaker's yard, might find their way back onto vehicles running on the network, though I'm not sure whether the objection is that the market price would be undercut or un-certified parts would be in use. Preventing enthusiasts buying momentos is not the primary aim, but 'collateral damage'.