My understanding is that 98 has a far lower Ethanol content. Ethanol has detrimental effect on plastics and rubber i.e. Petrol filler tube, plastic section of petrol cap etc. on my bike the Ethanol swells the plastic on the filler cap to the point where you can't get it off ! It has to be regularly sanded down to keep it free. Common on KTM bikes. The Morgan has a tight fitting plastic cap, I worry about it swelling and jamming.
