First order of business would be to find the leak.
Check if the system holds vacuum at the check valve on the firewall ahead of the brake booster. One line goes into the cabin, the other line goes to a reservoir. Check both. I suppose you should check the third line which leads to the vacuum pump to make sure you're getting vacuum in the first place.
Next check the vaccum switch bank. Unclip the right kickpanel, remove the right lower dash panel, remove the right transmission tunnel cover. There'll be a slender box with 7 vacuum lines attached to it. The vacuum source, if you will, is the top connector. No need to check this line if the system holds a vacuum. Check each line to find which actuator/s are bad. Note that one of the lines splits downstream of the box to the center vent actuator and one chamber of the defrost actuator. See if you can follow the line to the tee to check each actuator independently.
To get to the actuators:
Recirculation - two dual chamber actuators behind the glove box.
Deforst - one dual chamber actuator at the top of the ACC stack. Helps to have the glove box out.
Center - one single chamber actuator behind the ACC control panel.
Footwell - one single chamber actuator below the center actuator.
Diverter - one single chamber actuator covered by the left transmission tunnel cover.
I can go into detail of how to get to the actuators if necessary.
Replacement diaphragms are available for something like $5 each so there's no need to buy whole actuators.
Fixing the odometer will be a piece of cake by comparison