Ok ... I found SAE 2016-01-2252 which did a big study on how ITV deposits are formed. Go Google and search for "formation of intake valve deposits in gasoline direct injection engines" and look for "oil-club.de" and it has the full PDF download - should be near the top of the search.
From the SAE study, they determined the majority of the deposits was flow from the PCV system, and when they removed the PCV system all together the deposit rate dropped to near zero. The IVD rate on the individual valves was also a function of the PCV gas introduction location in the intake vs the location of the valves. The valves closest to the where the PCV gasses came into the intake had the largest deposits.
View attachment 145157
They also tested for the impact of bad valve guides and seals, and really didn't see much impact on a new head with new guides and seals compared to what they considered a worn out head with supposedly worn guides and seals. See section called "
Blowby versus Valve Guide Leakage". Most of the other 29% in Fig 10 might have been from bad valve guides and seals.
"A new head with unused guides, new seals and valves was used in Test No. 3. These data along with the data from the prior two tests are summarized in Table 2.
While directionally higher in average weight gain, a close examination of the individual valve data shows no pattern that supports a conclusion that the new head had higher IVD formation."