I have a friend with a <tdi 300 auto and her steering was getting heaving and a bit graunchy - when I checked the pas fluid level was low so we bought a bottle (1ltr I think) and put almosy ALL of it in the pas reservoir!!
There can't have been hardly any fluid in the system, no obvious leaks, a bit of misting on the pipes but nothing horrendous. Was serviced by professionals (the robbers) 6 weeks ago!!
After that I checked the air filter and guess what, it (the filter) now resides in an auto musiam, the thing was prehistoric !!!
Professional eh, we know best - like hell you do.