@Sacto Mitch yeah, I know it’s not ‘dirt’ in the sense of ‘pick it up out of a ditch’ dirt. I’m pretty sure it’s dried up, crystallised fuel from lack of use. Googling it, I find this useful article about stale fuel converting to peroxides and gum. A common risk with ‘occasional use’ vehicles I guess. Worse still in lockdown where no-ones driving anyway!