I want to do color modulation with oils on base coat panzer grey.Any advice would be appreciated.

Look for oil weathering on the web.

Here is one.

https://www.youtube.com/watch?v=WyQeb1rvZV0

Cheers

Because of the opacity of oils, I'd suggest going with lighter colors than you think you need. Like, I use Abteilung 502 Faded UN White for doing highlights on most colors. I use a 502 blue copper oxide for highlights on Panzer Grey (I like the blue tones).

Other than that, you may find you need to do everything in one pass. Because even if you come back a week later, oils may not be dry, so additional work may remove previous oil techniques.

https://www.youtube.com/watch?v=7IkBFWzwJ-s&list=PLZ9GDtkHYnVmc3b8ttF5cyh8MiOWZ-e33

This series, by Wilder should help.

Mike Rinaldi is the King with oils search is videos or the Tankart books (best books ever) you can find also some post here in armorama from im and on track-link you can find a Rinald articles about that

Isn't the oil dot technique a form of color modulation? There should be a few posts about the oil dot technique for Panzer gray.

https://www.youtube.com/results?search_query=mike+renaldi+oil&page=&utm_source=opensearch - Rinaldi

This is the article i talk before...

http://www.missing-lynx.com/articles/other/oilpaintrenderingmr_1.html