Would the use of an o-ring sealing ring add too much bulk to the assembly?

The use of o-ring sealing rings does indeed increase the volume of components to some extent, but this increase is usually relatively small and mainly concentrated in the sealing groove and its surrounding area.
The O-ring itself is a circular rubber component, and its thickness and diameter are designed according to sealing requirements. When it is installed in the sealing groove of the component, it will occupy a certain amount of space, which naturally leads to an increase in the volume of the component in that area. However, this increase is localized, and due to the relatively small size of the O-ring, its impact on the overall volume of the component is also limited.
In addition, it should be noted that during the component design process, the installation requirements of the O-ring are usually considered in advance, and sufficient space is reserved to accommodate it. This means that the volume of the component has been adjusted according to the design requirements before using the O-ring. Therefore, in a sense, using O-rings does not "add extra" volume to the component, but rather considers this volume as part of the sealing design.
In summary, although using o-ring sealing rings increases the volume of the component in the sealing groove and its surrounding area, this increase is relatively small and acceptable. In the design and manufacturing process of components, it is usually ensured through reasonable layout and size planning that such additions will not have adverse effects on the overall performance and use of the components.