Hello all,
Many thanks for the tips
Was not so, bad nor encrusted, just a soft brush and gently blowing, then isopropyl alcohol. About ESD the scope was grounded, damp and rainy weather.
The upper Rear casting by HV section had embedded brown deposits, metal corrosion, I used fine steel wool!
Next to clean the HV to CRT connector and lead, then perform the CRT, HV and Z axis calibrations.
Enjoy
Jon
Jean-Paul