Shimano brake lever compatibility

Hi everyone

I recently discovered that the right brake lever of my bike leaks oil. If I refill it and go for a ride after it goes fine. The problem comes when I go check it the next day and it's always covered in liquid. I've search for some information and turns out that this is an old model and I can't find a replacement lever. Trying to fix the O-rings in the piston wouldn't work either because as I saw on a tutorial it would be necessary to brake the pin that holds the lever together and it would be hard to put it back together (It doesn't have the screw that loosens the pieces to disassemble the brake)

My brakes are Shimano Deore BL-M615. I thought of replacing just the handlebar piece (Shown in the picture) with another Shimano model. My question is if there would be some kind of trouble if I change only that part but I don't touch the caliper. I can't seem to find much information of Shimano brakes compatibility

Thanks in advance!