I got really, really good results (more or less "as new" condition) on my wifes convertible with the following:
1. Scrubbed with a medium-stiff brush and a very strong mix of shampoo. Rinsed very well with buckets of warm water.
2. Renovo black Soft Top Reviver. Painted on with a brush fairly generously, overlapping the lines. This stuff is almost like a dye. Its a bit expensive though.
3. When bone dry, a good spray of Aerospace fabric guard all over - Rain water beads on the fabric like a waxed bonnet after this stuff.
The only draw back to this process is the drying times between products, which might make things difficult on a one day detail.
PS... I wouldn't spray a hood with a jet wash, unless it was on a weak setting.