Did you get the mushroom plugs from an auto-spares shop? I had thought they were only for "professional" use. Mine seems to be holding fine at present, but I last night I noticed a far more serious problem - oil leaking from final drive, and also for last few hundred miles has been making a little noise. Not sure how imminent a failure now is - frustrating as I'm only about 500 miles from Ushuaia!
I had heard bad reports of the cops in N Peru, but had no problems myself. They seem to lurk at the outskirts of every town, but are easily spotted - always parked very visibly and sideways. I take it you've not been so lucky!