Oil from Kitniyos - Mayo & Marg
these do not require special KLP certification
הגה ויש אוסרים [קטנית] (טור והגהות מיימוני פ"ה ומרדכי פ' כל שעה) והמנהג באשכנז להחמיר ואין לשנות
מיהו פשוט דאין אוסרים בדיעבד אם נפלו תוך התבשיל
וכן מותר להדליק בשמנים הנעשים מהם
ואינן אוסרין אם נפלו לתוך התבשיל
משנה ברורה [י
רוצה לומר שאין צריך לדקדק לתלות הנר של שמן במקום רחוק מן השולחן משום חששא שמא ינטף על מאכל
דאפילו ניטף אין לאסור דבכגון זה לא נהגו להחמיר כן מבואר בדרכי משה
ומסיים עוד שם דאפילו כתשו אותן השומשין שעושין מהן השמן במכתשת שכותשין שם חמץ נמי לת לן בה
והטעם דאפילו נתערב בו משהו נמי בטל בששים קודם הפסח
ואין לומר שמקבל טעם מהמכתשת של חמץ דהא צונן אין מפליט ומבליע
Pure, clear, cloudless oils derived from Kitniyos, are not, and never were, prohibited by the Kitniyos decree.
An analysis of the Mishneh Berurah, OCh 453 MB 11
The Rama  rules - During Pesach, we may hang an oil lamp burning Kitniyos oil even though it will likely drip into our Pesach food.
The MB explains - although the risk is significant, it is permitted because the Kitniyos custom was not created or applied to these circumstances. This is the ruling of the Rama in his Sefer Darchey Moshe.
MB quoting and explaining the Darchey Moshe says - this is permitted even where there is a risk that some Chamets crumbs might now be in that oil and by soaking will be contaminating it with Chamets taste, this is not a problem. [for example - sesame seeds that have been pounded in a mortar that has been used for Chamets]
The MB explains that it will be Battel before Pesach begins.
The MB adds that actually there is no problem in the first place because sesame oil is not sharp and will therefore not absorb flavour absorbed by the mortar.
The MB is concerned about the flavour absorbed by the mortar but not about crumbs or specks of Chamets in the mortar. This is because only the large mortar might have adequate mass and therefore absorbed flavour, to disqualify the oil. There is no suspicion that actual crumbs or specks of Chamets may contaminate the oil because A] that risk is negligible and B] even if they are present they will be Battel.
The sesame oil under discussion was a very crude and cloudy product, thick with pulverised sesame. And yet, such oil may be placed even where it is likely to drip into our Pesach food. Why? Because the Kitniyos decree was never promulgated to prohibit this form of Kitniyos. It banned the use of actual Kitnoyos or flour derived from Kitniyos.
Darchey Mosher Tur 453:2
Kitniyos may not be eaten but they may, unlike Chamets, be stored in one's home; they need not be sold with one's Chamets.
They may even be kept in one's home if they were soaked in water [this was a common practice in those days, today we call this process 'malting' which is an essential step in making beer and whisky and high fructose corn syrup] unlike wheat which becomes actual Chamets and must be sold before Pesach after becoming wet.
The question is - if we treat Kitniyos like wheat and barley, and that is why we do not eat them during Pesach, then why are we permitted to keep Kitniyos which have been soaked in water?
The answer to that question is that the decree was not crafted to apply broadly to prohibit whatever is prohibited as Chamets: it applies only to eating - we are simply not permitted to eat Chamets.
The DMoshe continues saying - "and in the same manner it is permitted to use oil derived from Kitniyos - and if a seed is found in one's food the food remains Kosher for Pesach" [however, it seems that the seed must be removed - and this is consistent with the MBerurah we referred to here and here]
From his thought flow, he seems to be describing that the seed dropped into the food from the oil lamp.
He continues with the ruling of the MaHaRiL that one must not use an oil lamp charged with Kitniyos oil where it may drip into our Pesach food. Furthermore, the MaHaRiL prohibits even if the oil is not Kitniyos oil but the lamp was previously used with Chamets oil. [The issue seems to be that the entire lamp is deemed to be a Keli Rishon - like a pot that is cooking on the sotve, because the flame heats the oil in the lamp reservoir. I presume that it is deemed to be Chamets because it would not be unusual for the diners to reach up and dip their bread into the oil of the lamp.]