[PhilippeDM]

Roger,

According to JC Mermet, the motor cowling you refer to is from type 041. He add this description: (my translation)
'These are the same cowlings as for type 40 with a DB 605 A engine, but with the big 50 lit. oil tank. This cowling was exclusively used by Bf 109 G-14 with werknummern between 462000 and 464000. Those aircraft were produced by Erla Leipzig in parallel with BF 109 G-10 equiped with DB 605 D engines. This explains probably the use of the big oil tank on DB 605AM engines, to simplify the engine production, to avoid an unnecessary diversification of the accessories delivered by subcontractors'

Clear drawings accompanies this text.

The same occurs to cowling Type 061, where the assembly line uses DB 605 ASM in conjunction with DB 605 AM and two oil filler points are present.

Also to be seen on Type 100 cowlings for DB 605 D engines (Bf 109 G-10 (WNr. 130000); Bf 109 G-10/U4 (WNr 610000 to 613000) and Bf 109 K-4) The oil tank has now a volume of 60 lit. And finally on Type 110 and type 111 cowlings (WNrs between 150000 till 152000 and 490000 till 491000, produced exclusively by Erla, engine DB 605 D.

All those cowling types bear other differences, but I tried to resule the oil tank issue.

Hope this helps.

Source: Mermet, Jean-Claude - Messerschmitt Bf 409 G & K, Editions Caraktère, Hors-Série Aéro Journal N°1 - 07-08/2008