Ok have a 2001 blazer fuel sending unit is bad installed a new one but can’t close it up due to the round o ring that came with it have greased it down along with the opening but can’t get it to go down enough with the ring attached to get it sealed! Any bright ideas?

ok the old ring was a L-shaped flat ring which is bigger than the new O-Ring the sending unit is also wider for the flat l-shaped ring so can not use the new o-ring has a lip on the underside of the sending unit so as you press down on the ring slips up on it sealing it up! However it’s very hard to press the seal and sending unit down into thank getting it to seal! I did grease it up and then heated up the seal make it softer but over night had s cold snap come in and can’t get it to seal. It will take at least two extra people to get it in and secured by my guess!
now I have 2 brand new unit replacements all made the same way all going to the round o-ring and no flat l-shaped talked with him dealer they stopped making it after 2001 only sell the round ring took mine and checked it to there’s and there the same size. They told me it’s a very well known problem but gm has not made any attempt to correct the problem!