(Admin - feel free to move - I placed it in general to hopefully get a wide member sweep.)

Oileak, I've been riding Harly's since the late 70's & they have all used that style cap, but all mine have had a dip stick built in, to measure oil level.i have never had any problems.

even with the oil in tank a flex magnet will pick up ,as long as what ever is there to pick up, [screws,washers ?]is not stainless.with out a dipstick how is the oil level measured?good luck with the search.

The oil tank pipes normally stick up an inch or so in the tank itself.  This is so chit and crap collects on the floor of the tank and does not get drawn into the oil system and pump etc.  As mentioned use a magnet to see if anything is there, but if it was me I would be draining the oil, removing the tank and giving it a full flush with kero or the like - just so I can sleep well at night.

Hi all.  The plug in the pic is an aftermarket 'plug/cap' only. My (then near new but used) bike never came with its stock factory dipstick. I dont have an original one. I have never used a dipstick and fill my level bike to just below the base of fill pipe if this makes sense. This places the oil just about perfectly where it would be if dip stick tested. Has worked fine for 24 years. Visual is easy and clean.

I get yah.  The issue I see is that if its a generic eBay plug and cover, while different types and brands may all 'look' the same they could in turn use way different mounting methods like you said - glue or a screw etc.  I see where your comign from; just because there is a thread there does not actually mean it was used per-sec, but you may have no choice and have to just assume worst case.  

Also thought I'd say, I hope when you do a service and change oil you make sure the motor warm and drain the tank soon after riding, as if you just top up tank to just below the top. you might find the crank case has oil laying in it. & when you start motor oil pump brings the extra oil from crank up to oil tank, you could have trouble. just mentioning as can happen.

Thanks mate, never been a hassle in a coupla decades. I am also a touch anal and change the oil and filter every 3000klms.

Ask the supplier what materials are in the plug.

Agree with Wideglider, ring supplier or order another plug & inspect it. Hope it wasn't from one of those places that takes 6 weeks delivery

Advise taken - I just ordered another and will see that holds it together.