Outer Limits 4x4 Board

I'm now on my second v8 starter and its playing up. They are only the cheap $220 after market ones from Ashdowns but I'd assume they'd last more than one offroad mud trip. First one failed slowly, this one now just clicks when I turn the key, then after serveral tries it will turn over and fire up. Battery is brand new so it not the issue.

What other things could be causing a problem, wiring...?

What things should I test and how?

I pressure clean the car after each trip to minimise buildup and I put a dab of silicone around where the starter meets the engine just to minimise water getting in.

pull it out and strip it down it will be full of mud and oil and shit mine was. or it could just be a cactus solinoid

I would have thought they'd be a little better sealed than that.

When pulling apart do you have to replace parts or is more likely to just need a clean out?

I've got 3 starters (2 x lucas, 1 x cheap aftermarket) plus the one in the car. Other than putting them back in, is there a good way to test the starter and the solenoid?

i put mine back together with a heap of sealer around where it screws together but mines an old lucas and leaks like a siv to test it wip it out and throw it in a vise and use that as a test bench with a good battery just earth the vice to the batt and ise the pos on the soloinoid