Originally Posted by Plaka
I don't have any problem with the pushrod tubes on my '83. Tapped them completely out of the jugs with the drift, switched them intake for exhaust and put them back with soft face hammer. The depth is totally noncritical, Set them too shallow initially and then set them correctly with the drift after torquing the heads. The tubes are a slide fit in the jugs, not the heads. Didn't notice if the rings on the tube were brazed or welded. Don't imagine it matters. It's not like you are putting big force on them. if you have to, the seals are too hardened and need replacing.
When I braze stuff the strongest rod I use is Harris 56% silver. The metal will fail before the joint ever does. I imagine BMW can do as well or stronger. Welding can actually make a weaker joint.
I agree with you (strongly) on the mechanical overload thing. I mention the matter because it doesn't appear on maintenance schedules but is pretty important given the age of the machine. Worth checking out at next opportunity, takes only a few moments. if one is frozen, no biggie, just walk away. Put a new nut on the shopping list and work it into a parts order somewhere. When an opportunity presents with someone experienced at cutting them off at hand, then deal with it. Nice off-season project. The important bit is getting it on the radar.
You can pull the heads without touching the exhaust nuts, if that needs to be done. So you can replace the push rod tube seals without touching the nuts. To be kosher, you do replace the 3 sealing o-rings at the base when doing the pushrod tube seals and of course the head gasket. You can do it without totally pulling the jugs but it isn't the best way to go unless you are very broke/pressed for time.
As has been mentioned, unless there is massive leakage at the seals, it is a trivial matter. You can leave it until the pushrod tubes are getting rusty and then deal with those at the same time. The exhaust nut threads in the head are very not trivial. If there is corrosion going on you really want to preserve those threads. A year or so won't matter much but it is a fix sooner than later kind of thing.
I could see maybe leaving the header on IF I didn't have a crossover. Other than that, it sounds like more trouble than it's worth.
I think installing pushrods like that is just asking them to leak at the cylinder. They are touchy enough there as they are. That is if you are not like Plaka. He doesn't consider an oil an oil leak until it is leaking enough to wash the parts involved clean. Personally, that's right when I stop calling it a leak and start calling it a gusher.