The way to proceed would be to start out with a complete list of all the machinery involved, the lubrication requirements of the listed equipment as per manufacturer, whether in practice the manufacturers recommendations are actually followed or not and what the reason is for the non-compliance. That would give you a complete database of machinery, recommended lubricants and actual products used and knowledge whether or not manufacturers recommendations are strictly followed. You can simply write down such a list, use a database program or a dedicated maintenance application. It will however take considerable time to gather all the information needed, and some may not be easily accessed or may not be obtainable at all. Whatever method used - you will end up with quite a lot of information, now ordered in such a way that it is easy available.
One of the things you will have is a list of lubricants in use. The first step then is to look whether there is some overlap - and whether maybe a higher spec product could be used as a substitute for two or more original products in combination with extended drain intervals. From that moment on you should contact your lubricant supplier to help you make intelligent choices regarding to product choice, whether regular oil sample analysis would be of value and what oil change intervals would be optimal.
The whole exercise can be quite time consuming, especially the not so sexy data gathering part. However you should bear in mind that the outcome may only be as good as the data you put in: "rubbish in leads to rubbish out".
