Dave, that`s on mine as well, and possibly was on my others. It appears to be from not having mudflaps fitted, the spray from the rear wheels has pitted the paintwork, You`ll have to get the mop out to deal with it. I`ve the exact same and I borrowed my mates mop for when my 3 months recoup is over :D
Re: the servicing.....I have a very good mate who`s a Merc engineer and he knows these motors very well, he`s serviced and worked on all of mine and is very reasonable. Did the head gaskets on my old 78 OB for £400 when i`d been quoted 2 grand from the local ford (Fraud) dealer.
Probably £100 ish......will let you know.