Missing transaction for 3 days, please help!

[leogon]

I've sent 0.988 coin from my MultiBit 0.5.16 wallet (which is now an outdated version) to my Coinbase wallet, leaving the 0.0001 transaction fee in my wallet so that after sending, the MultiBit wallet contents would be zero. It has been over 3 days and the transaction is still pending/unconfirmed, and has been seen by 8 peers. It has not appeared as a pending transaction in my Coinbase wallet, although I sent 0.001 from the same wallet a few days ago that went through fine within a few hours. Can anyone give advice on what I should do? Thanks