All good points from Lanval.

I'll add a bit...

1) Find the angle-bent flat blade spring that the odo reset button stresses against. This spring provides most of the pressure you feel when pushing. There's a coil spring or two but they're not as significant.

Use needle-nose pliers to take some of the bend out of that flat blade spring to reduce the tension the button has to work against. The button is actually L-shaped and can't take the stress. I've never had to replace an odo button a second time. I use mine every fillup, and drive 600-700 mi/week.

2) Unless you have a tach, find the red + white wire behind cluster, tie it up and mark with "FOR TACH ONLY". Do this when you pull out your cluster. Connecting that wire to anything but a tach can kill your cluster.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.