Digital BW, The Print

I am working on y stylus 1160 with MS FS neutral, after a relatively 
inactive period with little photo printing with the same ink bottles 
since more than 1y at least. 

Is it too long? I am getting clogged nozzles regulary, a nozzle 
cleaning cycle will purge it again, then after a short while it 
starts again - could it be the ink is become too thick?

thanks in advance, Bernie