Switching oil made leak worse?

[cross6]

2004 V6 Flex Mountaineer, 163K miles.

Been using either GTX or Motorcraft 10w30 and Motorcraft filters in my truck for the longest time.

I've had a tiny leak at the rear main seal for a while. For years. Maybe one drip every 3-5 days if I left my truck in one place. No big deal.

Well, I wanted to increase my oil change interval so I switched to Mobil 1 Synthetic High Mileage and M1 filters.

All Autozone had at the time was 10w40 in the M1 Syn High Mileage, but I've seen enough oil test reports to know that M1 starts thinner, and ends thinner than most conventional oils. So I figured it was probably close to the 10w30 GTX I've been using. No big deal.

Well I'm about 1,800 miles into this change and my rear main seal leak suddenly got dramatically worse. Several drops overnight, and it's coating the front of the tranny pan and tubular crossmember.

So. Is this just coincidence? Or did switching oils filter make a 3-5 year old leak suddenly worse?

 

[rlb81]

Is this just coincidence? Or did switching oils filter make a 3-5 year old leak suddenly worse?

I'm not sure that there is hard and fast proof, but this seems to be a general consensus: Most synthetics (M1 included) are much more detergent that regular oil, which means it will clean away any built up crud that's formed around your seals & gaskets over the years. So it's possible that the switch could have made your leak worse.