Yep, it's not the case cracking thing, just a cover. In you case it looks like the heater is contained with 3 air breather holes, there's no oil in there. So it's fair to assume the the leaking is as you figured - through the bolt holes. If it were me I'd get shot and replace with a plain cover*. You can also get covers that take an oil temp sender which could be handy. * I wouldn't bother if it didn't need removing to seal anyway.
I bought the temp sender cover off eBay, it's worthwhile, there's also a new seal available from the usual places. The sender isn't expensive and the plate has a blanking plug installed anyway. I think the chap who sells them is boatyardbusses, or similar id.
I haven't seen them for the type4 cover with just the two bolt holes mate. Sent from my SM-G981B using Tapatalk
Got some they stopped the bolt holes leak but I've still got a weep from the plate itself so just ordered an o ring. Sent from my SM-G981B using Tapatalk
If you're going that far (draining the oil) why not get a proper plate and get rid of that junk you'll never need dangling off the engine? If you want oil temp gauge the plates with the fitting look good to me, It's quite difficult to find a good location for a temp sender - I have mine in a sandwich plate I added for the cooler but if I didn't have that option I'd have done that. Maybe you already have that covered I don't remember.
Seen it mate cheers. I meant one with the central hole for a temperature sender. Sent from my SM-G981B using Tapatalk
Can't think of one, it's an option, some type-1 folk do this. Given the option I'd rather have it somewhere else and leave the drain plug purely for draining oil.
I'm going to see if I can get this heater plate to seal first Mick as it's original from the factory. (Swedish dorka) It fits in with the black overriders and headlamp washers. Sent from my SM-G981B using Tapatalk
The one thing you do know is that it was able to be sealed up somehow originally - to last at least the time between purchase of the heater and the warranty on the heater running out. There was a sump heater on sale at Volksworld in the swapmeet.. I didnt ask the price.