Problems after swapping non-SKS fob electronics to new shell

Hello all; first post here.

I acquired a one-owner 2009 a couple of weeks ago. It generally seems to be in great condition, but all three buttons were long gone from the one-and-only fob (non-SKS) so I ordered a replacement shell through Amazon.

I cleaned all the accumulated grunge off the circuit board using alcohol spray and an old toothbrush, before installing it into the new shell. I also transferred the RFID chip, the little white plastic spacer, and the new battery I'd put in about a week before.

Now the lock/unlock function is unreliable. Sometimes it works fine, but other times it just sets off the alarm instead. The alarm button on the fob turns it off for a few seconds but then it starts up again. The lock and unlock buttons don't seem to do anything at all while it is in this alarm mode.

The metal key still opens and locks the door. And the fob still works fine in the ignition, since the RFID chip is independent of the other electronics.

I am figuring I will have to open it up yet again and blow out the pushbuttons and circuit board with compressed air (maybe I pushed some crud in there), but perhaps someone here has some other suggestions from experience?

Many thanks!