Toscano's in Los Banos is one of 4 RV stores owned by same family. Primary store and main service facility with Airstream parts and expertise is in Manteca (Manteca Trailer Sales). They also have store in south Sacramento and near Fresno. I've not had work done there (haven't needed it yet...) but I've visited a number of times (tire kicking and trailer shopping) and their shop looks quite competent, and they were doing major chassis work and re-skinning on trailers.. Andy ?? handles parts and service items for Airstreams at Manteca location at 209.239.1267. Web site is http://www.mantecatrailer.com/
Having visited Los Banos, I'd take work to Manteca if it was anything significant, as Los Banos is primarily a sales lot...