Ultraplex 40max

hi all any ideas why my plex when recording suddnley slows down causing bufferunderuns

How old is it? it may need cleaning.I had same prob and cleaning the lens solved it. Or if it is only on certain discs the discs may be have a lot of read errors

Thanks for answer

tried cleaning no better it is fast for a while then just drops spead
for no reason could be old age