Love this forum - people are so helpful. Many thanks to all those who have taken time to help me. A special shout-out to Jay at Mercland - which other dealer do you know who is trying to help 3 years after I purchased? Wow, just wow!
Looks like it's down to three options, decision will be governed by available finances.
1) Keep rims I have which will be refurbed with 2 new identical front tyres (rears are fine). After all, the two front rims have been different for over 3 years now (3 years MOT passed) with no problem at all. And the odds of a tester identifying the different rims must be remote in the extreme. Yes, I know not ideal but have already incurred £150 cost toward the refurb which will be an additional cost to any other option
2) Get some genuine 18" MB rims from ebay (if the seller in Guildford is happy to ship to Preston) which will need refurbing. They have good front tyres at 7mm but that saving will be negated by the costs already incurred above. However, I have been offered a contribution to the cost
3) Change to 17" MB wheels which I have been offered by Jay. Just waiting info if they need refurb and/or new tyres
Outsider: Look on FB Marketplace which people have suggested. My problem with that avenue is I may be buying something damaged and of course, no comeback
Any and all comments welcome. I mean, is it the end of the world to change 18" to 17"? As Mrs. Gollom said, it's only an inch........