designjet755 cutter problem

[Gar the pilot]

My client has a Designjet 755 that cuts normal paper okay but has a problem with the first 6" of lite stuff. Velum or traceing paper it will intermentantly rip/cut the first 6" and then does fine. the cutter looks fine and as it cuts normal paper okay I am thinking it has something to do with the real it cuts against. Is the rail a replaceable part and how long does it take?? I have mostly done Belts on these and not much else.
Her prevous DJ 750 did fine with the ;ite stuff but has error code "0603A 0018048B" and code 10032-0070AD9. she thinks it may be main board related and not worth repairing.
Thanks

[Hewlett Slacker]

id replace the cutter first, easy enough and do get dull, then go from there. the one errors might be the carriage/trailing cables so check that. the other is a line sensor not seeing the mark encoder, also related to that as well.