Hi,
Milwaukee [http://documents.milwaukeetool.com/TIY383%20-%20Grease.pdf|specifies] using [https://www.ebay.com/itm/112134863665|Type E grease - part # 49-08-4122] for the drill. Scroll down to find the Milwaukee model number i.e. 1675-1
The supplier is an example only to show the cost, search online using the ''part number only'' to find suppliers that suit you best.
The user manual for the drill also mentions to only pack the gear case 2/3rds full with grease.