I just checked and I could get to my old transactions on XStreet, I have no idea when they will go away but for now this is how I was able to get a csv of all date from 2007 til I think 2010 when we were migrated to DD.
Go to your Merchant Homepage.
Click Magic Box Status in the list on the right side.
If a Window pops up asking to take you to the new marketplace click Cancel and that window will go away, leaving you on the old XStreet page.
Click on Sales.
Put in the Date Range you want and click Update Results
Click View CSV Output
I should say thats just for Sales, for purchases I believe LL has directions for both on this page https://community.secondlife.com/t5/English-Knowledge-Base/Viewer-managed-Marketplace/ta-p/2854226