Have about 58,000 mi. on the 2003 GMC Duramax I bought in Feb., 2003. Have run Shell 15W-40 Rotella T conventional oil up to now, but considering switching to Amsoil synthetic 15W-40.

Experienced a leaking seal recently when I switched from conventional to synthetic on an older (1979) motorcycle. I'm thinking the old '79 seals weren't up to synthetic.

Anybody think I may have waited too long on the Duramax to switch and may suffer leaksas well?

Thanks in advance for your input.