I also run into deterioration of my 10W laser wood cutting performance. Suddenly, 3mm could not be cut properly anymore and the laser spot size obviously increases quite a lot. First, I thought it may had been caused by uneven wood plates with the focus being off or inconsistency of the hardness of the wood. But looking at the lens the reason was quite obvious. I cleaned mine by soaking a cotton swap in an alcohol pad and wiped the lens clock-wise as described by the user guide. This did bring back the cutting performance for me.
