Will it affect the running of the Discovery 300 dti if the Tachometer is not working?

The Drivers front electric seat on my 1997 Discovery will only move forewords to the steering wheel and not backwards towards the rear of the Vehicle, are there any fuses that might have blown or is it possible to move the seat back manually.

This is my first post, the throttle spindle seal on the Tdi Injection pump is leaking Diesel, where can you get a new shaft and the brass bush from to do the repair, it’s on a Discovery 200 DTI J Rej, I have got all the info on how to do the job, it’s just the replacement parts that I want...