Queries about synthetics and seals?

Hi all, hope all have had a good new year!
Changed my belts last week before a trip down to the coorong. All went well but while I was underneath the front end I noticed some oil around the front of the sump, on closer inspection I found the oil seems to be coming from the front crank seal aaarrggghh!
Was about to go whoopieeee when my cousin mentioned that it may not be that bad, it does not drip and I have left cardboard underneath it after a drive to make sure.
He said that some fully synthetic oils can weep through these seals?! Can anyone in the know shed some light on this as it has got me worrying and although I can replace it in a weekend with my cousin I hate to think how much bourbon I'll need to take round to convince him to help out.
Cheers, potsy.

Sorry, probably best to add that I'm using Caltex delo 400.

I have read the zd are shocking for weeping threw the rocker cover or timing chain and down the front of the block..

But I've just read you have a td42 so scratch that..
Um well I've run delo 400 in my td42 for about 10 years when it was on the farm..
It was our main truck oil so had it in bulk 44's and used it all our deisel engines..
But can't say we have noticed any leaks from the front end sorry bud..

nah delo has been in my td42 for 20 odd years not a seep, nothing. i'd guess that a thicker oil might slow it down.

Cheers for your input fellas, the car was sitting around for a while before I bought it as the owner passed away so I think the seals may have dried up. have come to terms with it over the last couple of days and will just strip the front end and change it along with idler pulley on ac, radiator hoses and the umpteen other things I know I'll wanna do while I can get in there :) wonder if I can squeeze a HPD front mount in there while I'm at it......one day