Also, you don't say whether the new starter solved your problem, and the garage was only advising you on the oily solenoid. It sounds as if they did only what you asked them to do - change the starter. To deal with the other problem may have meant other procedures like replacing a sump gasket or tightening bolts etc to prevent oil leakage.
So, the garage may not really be as 'iffy' as M in B suggests.
If it was my car I would get underneath ( safely), tighten the sump bolts, clean up the contaminated areas and tighten any bolts near the solenoid which could be allowing oil to leak and be splattered everywhere. You should not need to replace the solenoid if it is functioning efficiently. Or, you could get the garage to deal with it at about �40 - �100 quid an hour !
Good Luck, and remember to give as much information as possible so that people can give you accurate information. There are some very knowledgeable and helpful users on here.