Outer Limits 4x4 Board

hey guys i need some help real quick my altrernator isnt charging my battery(i think) the dash gauge reads about 10-11 volts,
i have 4 questions
1. is it what my battery is putting out or my alternator on the gauge? (newish battery has been recharged)

2.i have some friends with a tb42 and sd33 spare alternaotr would that fit my td42?

3. my mate tells me to take it out and spray it with the hose to flush out some dust/dirt/mud would that help it?

4. or is a new or reco'd one in order?

if its urgent , pull it out and match it up with the sd33 alt. If it wont fit ( id say no) drop it off at an auto elec and pick it up in the arvo.

why fart around when it can be rebuilt for $100-200

cheers