The reason the contamination enters the aircon/pressurisation system is that it comes from the engine or PU compressor and is unfiltered. the reason you may notice it more frequently about 5 minutes after touchdown would suggest the type you are flying on is more prone to APU bleed contamination than engine contamination.
This is a serious issue (I know - I've had it). It is likely to be a contributory or principle factor in many "human factors/pilot error" accidents and incidents.
Banning TCP from engine oils would be a start, as would fitting filters to the outputs of the aircon packs. Boeing's decision to make the B787's pressurisation air source separate from the engines and APU is indicative of their internal acknowledgement of the issue ad is a welcome step in eliminating the problem entirely. It is appalling that Airbus did not do the same on the A380 or intending to do the same on the A350. I don't think any new aircraft should be certified if it uses bleed air for the cabin/flt deck.