Our lead source is always a hot topic. I have set up a rule for when it is changed in SFDC and we get 50-100 day from merging records and the appropriate lead source not being selected. It has become unmanageable. We had our SFDC admin add Original Lead Source to the Lead and Contact but it is not pulling it in and is still causing errors. Weekly I have to take our closed deals "WON" and check them in the Opportunity Influence Analyzer to check for MOB and MIB. We do not have RCE set up properly and hope to in the next few months for attribution. More wonder if anyone has some tricks through Marketo with Smart Campaign that might help or a way to report on it without RCE.
Can you provide a bit more info about the rule in SFDC and how that is working? Also, how do you define Lead Source? Do you define it as the conversion point (form, list import, etc.), or the referral (AdWords, LinkedIn, etc.)?
Much like many things in Marketo, there are a number of ways to approach this challenge. We usually recommend a phased approach to getting your attribution in a good place; similar to a crawl, walk, run type of approach. Those steps would all be dependent upon the answers to the questions above.
Unfortunately we have no permissions in SFDC to see any back end rules, we only have basic permissions. We have many lead sources which can be Digital Ads, Live Chat, Web Forms, Website, Called Sales, Emailed Sales etc... we created the lead sources for our SFDC admin to add into SFDC.
I've written about this extensively. You have to spend a lot of time with it.
Marketing Attribution Setup Checklist - Marketing Rockstar Guides
Sounds frustrating! Specifically around the merged records, are those records being merged by people or some sort of tool? If it's a tool maybe there's a setting that can be changed to pull in the correct lead source. If it's that a bunch of people, like BDR/Inside Sales/SDR's have access and they're tasked with merging and they suck at it, then I recommend working with your SFDC admin to figure out who the people are making the wrong selections and fix through training (or worst case, remove the functionality from them if they can't be trusted).
We have our Sales team merging records as they see them or a SDR team who should be checking in SFDC for duplicates and merge it together. However it seems that has not been adopted as the process yet, so now we have a Sales Rep, SDR and a Data Intern calling out to the same Lead/Contact which is not ideal. We have no budget for a de-dup tool and have to reply on Sales to pick the correct lead source and manually switch when it hits us on our end. Our SFDC admin is aware and put the Original Lead Source in place hoping to solve the issue moving forward.
Based on this response and the above, there are a couple courses to action to take.
Let me know if you have questions. Thanks!