Surely it would be a huge help to know what it is you have there... V-8? 6cyl? 4banger? Carbed? Fuelie?
The backfireing can be caused by the timing slipping..
Or a badly burnt valve.. Or several other things.
The oil seal leaking.. Are you sure it is the filter seal? Or perhaps the gasket between the block and the filter bracket?
I feel sure the two problems are not connected.
Big JIm
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