speedo sensor sticking

i recently installed a new speedo gear because of a axel gearing change ( i know,OEM tech, but the sensor is still OEM ). the housing is rotated to reflect the larger gear. the problem is that the speedo seems to stick some times. if it is off too long the check engine light comes on which is normal. is there some way to clean the sending unit. the shaft seems to spin freely. i sprayed pb blaster into it and it came out rusty looking. then i sprayed in some teflon dry lube. it the sensor optical and did the lube block the sensor . or is it a magnetic pickup? the sensor likely is the original at 230000 miles. any ideas or do i need a new one.
thanks

We have the same (sometimes) problem with my wife's '91 . . . . it hasn't been enough of a problem for me to really check-out but, I thought, gee, if I reply and thereby move your post to the top, maybe we'll both get some hints . . . . . . . Don