Thanks Happy.

I had already done this, but it was still trying to parse some decimals as Currency, and others as Dates (which was inconsistent depending on which sheet I was getting the data from). I ended up using a Script Component as a source, and creating the connection in there to pull all the data through as a String, and then using a Data Conversion Transformation to get them to the right type.

Excel was a bit janky, and sometimes sent dates as ints, and ints as dates, but some tryparse's and dateadd's/maths fixed that. A struggle, but got the result I wanted.