Performed the 20k service on my 2018 TG today and checked and verified several things. Good news is that there is no indication of oil migration from the trans to the primary. I carefully measured each by draining them into a quart measuring cup. I drained exactly 32 oz from the primary and 27 oz from the trans. Withing spec. And while I changed out the primary at 10k this is the first fluid change I've made to the trans so what was in it is what it came with from the factory.
The magnetic drain plugs for the trans and primary were very clean and had noticeably less debris that what I've encountered on my other bikes.
The o-ring on the engine oil drain plug was pristine making me think that this motor runs cooler than some of my previous Harleys. I know for sure that on my 2012 CVO Ultra with the 110" Twin Cam the o-ring on the engine oil drain plug was very deteriorated at each fluid change and it appeared to me to be related to heat.
I've got my new Avon Cobra Chrome front tire, two fairly new Goodyear ComfortTreds on the rear and now a full service so I'm all set for the riding season. Let the fun begin.