I am going to get some hate for this post because it don't fit the excepted forum veiw.
I have a 2016 Pioneer 1000 with 4,100 + miles on, it lives outdoors all the time last summer I had took the roof off, had it off for most of the summer it never ever had a full P5 roof only 3 seater roof zero water intrusion!!!
I just changed the differential oils last night zero water intrusion,
I had water coming in over the floor on a stream crossing 4 weeks ago I have been blasting up and down a creek hitting the hole with speed I have yet to have any water intrusion.
I do not go swamping no ever intend to for normal stream crossing and splashing through the mud and water your stock vent tubes are fine, I would consider it a cheap insurance to make me feel good modd but not as important as it implied on this form.
When we where out in CO we crossed a stream that was all most up to are seat bottom so deep we had to help my son on his 300ex across because one end or the other would float down stream no signs of water intrusion.
Thought I should post a counter experience of the heard mentality of you MUST extend your vents or your machine will be water damaged when you use it.