hm.. lots of food for thought here - I have never kept the dob in any other position than vertical. That has now changed. Also I did the "every so softly" cotton wool thing going round the mirror from center to edge and although the mirror is looking so much better than before the spots remained.
Quick star test last night and have great diffraction spikes again visually, moon was very sharp also.
I believe the alcohol I used was not the cause - as i kept a close eye on the mirror at all times of the cleaning process.
I was also under the impression that isocol (used during the final stage to displace water left on the mirror) was 70% isopropyl alcohol dissolved in ethanol (no additives included apart from these)
Lessons learnt so far:
1. Never store a dob in the vertical position
2. Clean mirror more often than once a year!
3. Inspect all telescopes upon purchase and record condition of mirror/lenses for future reference
