My problems were simple - as it turned out and as is often the case with a running toilet - but I appreciated Roberto's courtesy, quick analysis and repair, as well as careful consideration of three other plumbing questions. Am glad to have his business card for future plumbing calls.
Postscript: One day later the toilet still runs on and A&D Marca has not responded to email or message. This was a very expensive lesson. Many days later A&D Marca did text back.