Depends when Castrol came on board.
Obviously they became our shirt sponsor in ‘95 but we’d had the half green diamond badge since ‘91.
As an aside and in danger of being the most boring post ever (albeit Reg would have approved), I always assumed that the change from Burmah to Castrol was just a rebranding at the sponsors request as they were basically the same company but Castrol was a bigger brand in the UK.