Rear half shaft oil seal leaking onto drum brake

Petrol hard top Jimny 2010 1.3VVT 80K
Thanks for all the combined wisdom and Dad humour on here...
​​​​So, just got the car for a bit of green-laning in Wilts and wife will drive round town hence had to be a small car... (she does like it too!)
Had a mech to check it over. He said it was in good condition generally re rust etc.
He noted the above and said oil was getting on the drum shoes nr side, prob ½ shaft oil seal. Likely as wheel looks a tad oily all over. I found that the diff breather cap seemed to be immoveable and couldn't shift it with screwdriver and hammer albeit at an awkward angle. Front diff cap spins. Is this the likely cause of the oil seal leak? Been reading re diff breathers but not sure we'll be hitting more than a foot of water so I'll get him to replace standard one when he fixes stuff. 
Also has a small engine oil leak he said may be thro the cam sensor? Is that a reasonable thing? 
Using a class 2 tow bar with a US-sourced (as rare) 1¼" hitch receiver (breaking strain 12000lbs), 6mm 5½ tonne soft shackle and ½" US Curt tow pin for rear recovery. Jimnybits HD front recovery points used with same soft shackles to be fitted. OK?
The tyres are newish Runway Enduro 726 but for road, labelled '4x4', not AT, so I'll keep them and see how they cope off road after reading Lambert's posts. Spare is a different AT so might change to road similar after reading the tyre info here and rotate.
Thinking of radius mount guards too. 
Would that be ok for Salisbury Plain avoiding mud holes (and Challenger 2s)?

If the breather on the diff. is blocked then a build up of air pressure within the casing - caused by the hot air expanding - won't be able to escape so forces it's way past the puny rubber seals on the half shaft hub seals taking with it an amount of diff. oil. You need to repair/replace with standard or fit a diff. breather kit that replaces the standard breather with hoses and pipes to vent the expelled air at a higher level. You can then clean/replace the parts of the drum brake that are contaminated and hope that this will cure the problem of further contamination re-occurring. If this fails to cure the leak, it is probable the the seals on the ball race have been damaged and then you are faced with replacing the bearing. For a competent technician with the correct tools this is a simple procedure taking a couple of hours.
When I had my SJ ( Gen.2 ), I modified the half-shaft and made a seal housing to eliminate the standard seals and replace with a twin lipped seal. This eliminated the problem and allowed me to wade through water up to 36" deep but this mod needs the use of a lathe.

Roger